diff --git a/changelog.md b/changelog.md
index 2af140fc61..672e093e35 100644
--- a/changelog.md
+++ b/changelog.md
@@ -2,6 +2,8 @@ Codion Change Log
 ==================
 
 ## 0.18.23
+### is.codion.common
+- JSpecify annotations applied to common modules.
 ## is.codion.common.core
 - ValueObserver.getOrThrow() added.
 ## is.codion.common.db
diff --git a/common/core/build.gradle.kts b/common/core/build.gradle.kts
index afdbe2945f..8d7e6340d2 100644
--- a/common/core/build.gradle.kts
+++ b/common/core/build.gradle.kts
@@ -1,3 +1,7 @@
+dependencies {
+    api(libs.jspecify)
+}
+
 tasks.register<WriteProperties>("writeVersion") {
     group = "build"
     description = "Writes the current framework version to a file available as a resource"
diff --git a/common/core/src/main/java/is/codion/common/Configuration.java b/common/core/src/main/java/is/codion/common/Configuration.java
index b751658b9c..7b70bfc251 100644
--- a/common/core/src/main/java/is/codion/common/Configuration.java
+++ b/common/core/src/main/java/is/codion/common/Configuration.java
@@ -175,7 +175,7 @@ public static PropertyValue<Character> characterValue(String key, char defaultVa
 	 * @return a configuration value builder
 	 */
 	public static PropertyValue<String> stringValue(String key) {
-		return stringValue(key, null);
+		return STORE.stringValue(key);
 	}
 
 	/**
@@ -196,7 +196,7 @@ public static PropertyValue<String> stringValue(String key, String defaultValue)
 	 * @return a configuration value builder
 	 */
 	public static <T extends Enum<T>> PropertyValue<T> enumValue(String key, Class<T> enumClass) {
-		return enumValue(key, enumClass, null);
+		return STORE.enumValue(key, enumClass);
 	}
 
 	/**
@@ -242,7 +242,7 @@ public static <T> PropertyValue<List<T>> listValue(String key, Function<String,
 	 * @return a configuration value builder
 	 */
 	public static <T> PropertyValue<T> value(String key, Function<String, T> parser) {
-		return value(key, parser, null);
+		return STORE.value(key, parser, Objects::toString);
 	}
 
 	/**
diff --git a/common/core/src/main/java/is/codion/common/Nulls.java b/common/core/src/main/java/is/codion/common/Nulls.java
index 24763b282d..71a58cfe2a 100644
--- a/common/core/src/main/java/is/codion/common/Nulls.java
+++ b/common/core/src/main/java/is/codion/common/Nulls.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Arrays;
 import java.util.Objects;
 
@@ -33,7 +35,7 @@ private Nulls() {}
 	 * @param object the object to check
 	 * @return true if the object is non null
 	 */
-	public static boolean nonNull(Object object) {
+	public static boolean nonNull(@Nullable Object object) {
 		return Objects.nonNull(object);
 	}
 
@@ -41,7 +43,7 @@ public static boolean nonNull(Object object) {
 	 * @param objects the objects to check
 	 * @return true if none of the given objects are null
 	 */
-	public static boolean nonNull(Object... objects) {
+	public static boolean nonNull(@Nullable Object... objects) {
 		if (objects == null) {
 			return false;
 		}
diff --git a/common/core/src/main/java/is/codion/common/Serializer.java b/common/core/src/main/java/is/codion/common/Serializer.java
index 8aa9d6005b..6633d617e0 100644
--- a/common/core/src/main/java/is/codion/common/Serializer.java
+++ b/common/core/src/main/java/is/codion/common/Serializer.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -39,7 +41,7 @@ private Serializer() {}
 	 * @return a byte array representing the serialized object, an empty byte array in case of null
 	 * @throws IOException in case of an exception
 	 */
-	public static byte[] serialize(Object object) throws IOException {
+	public static byte[] serialize(@Nullable Object object) throws IOException {
 		if (object != null) {
 			ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
 			new ObjectOutputStream(byteArrayOutputStream).writeObject(object);
@@ -54,11 +56,11 @@ public static byte[] serialize(Object object) throws IOException {
 	 * Deserializes the given byte array into a T, null or an empty byte array result in a null return value
 	 * @param bytes a byte array representing the serialized object
 	 * @param <T> the type of the object represented in the byte array
-	 * @return the deserialized object
+	 * @return the deserialized object, null in case of an empty {@code bytes} array
 	 * @throws IOException in case of an exception
 	 * @throws ClassNotFoundException in case the deserialized class is not found
 	 */
-	public static <T> T deserialize(byte[] bytes) throws IOException, ClassNotFoundException {
+	public static <T> @Nullable T deserialize(byte @Nullable[] bytes) throws IOException, ClassNotFoundException {
 		if (bytes != null && bytes.length > 0) {
 			return (T) new ObjectInputStream(new ByteArrayInputStream(bytes)).readObject();
 		}
diff --git a/common/core/src/main/java/is/codion/common/Text.java b/common/core/src/main/java/is/codion/common/Text.java
index ac7c46c32b..2db3c15bda 100644
--- a/common/core/src/main/java/is/codion/common/Text.java
+++ b/common/core/src/main/java/is/codion/common/Text.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.property.PropertyValue;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 import java.text.Collator;
@@ -73,7 +75,7 @@ public static <T> List<T> collate(List<T> values) {
 	 * @see #DEFAULT_COLLATOR_LANGUAGE
 	 */
 	public static <T> Comparator<T> collator() {
-		return collator(new Locale(DEFAULT_COLLATOR_LANGUAGE.get()));
+		return collator(new Locale(DEFAULT_COLLATOR_LANGUAGE.getOrThrow()));
 	}
 
 	/**
@@ -116,7 +118,7 @@ public static String leftPad(String string, int length, char padChar) {
 	 * @param commaSeparatedValues a String with comma separated values
 	 * @return the trimmed values
 	 */
-	public static List<String> parseCommaSeparatedValues(String commaSeparatedValues) {
+	public static List<String> parseCommaSeparatedValues(@Nullable String commaSeparatedValues) {
 		if (nullOrEmpty(commaSeparatedValues)) {
 			return Collections.emptyList();
 		}
@@ -150,7 +152,7 @@ private static String padString(String string, int length, char padChar, boolean
 	 * @param string the string to check
 	 * @return true if the given string is null or empty, false otherwise
 	 */
-	public static boolean nullOrEmpty(String string) {
+	public static boolean nullOrEmpty(@Nullable String string) {
 		return string == null || string.isEmpty();
 	}
 
@@ -159,7 +161,7 @@ public static boolean nullOrEmpty(String string) {
 	 * @param strings the strings to check
 	 * @return true if one of the given strings is null or empty or if no arguments are provided, false otherwise
 	 */
-	public static boolean nullOrEmpty(String... strings) {
+	public static boolean nullOrEmpty(@Nullable String... strings) {
 		if (strings == null || strings.length == 0) {
 			return true;
 		}
@@ -182,7 +184,7 @@ private static final class SpaceAwareComparator<T> implements Comparator<T>, Ser
 
 		private final Locale locale;
 
-		private transient Collator collator;
+		private transient @Nullable Collator collator;
 
 		private SpaceAwareComparator(Locale locale) {
 			this.locale = locale;
diff --git a/common/core/src/main/java/is/codion/common/event/DefaultEvent.java b/common/core/src/main/java/is/codion/common/event/DefaultEvent.java
index 1072e079f7..74948547a3 100644
--- a/common/core/src/main/java/is/codion/common/event/DefaultEvent.java
+++ b/common/core/src/main/java/is/codion/common/event/DefaultEvent.java
@@ -20,13 +20,15 @@
 
 import is.codion.common.observer.Observer;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Consumer;
 
 final class DefaultEvent<T> implements Event<T> {
 
 	private final Object lock = new Object();
 
-	private DefaultObserver<T> observer;
+	private @Nullable DefaultObserver<T> observer;
 
 	@Override
 	public void run() {
@@ -34,7 +36,7 @@ public void run() {
 	}
 
 	@Override
-	public void accept(T data) {
+	public void accept(@Nullable T data) {
 		if (observer != null) {
 			observer.notifyListeners(data);
 		}
diff --git a/common/core/src/main/java/is/codion/common/event/DefaultObserver.java b/common/core/src/main/java/is/codion/common/event/DefaultObserver.java
index 839622f66c..40a7d07f21 100644
--- a/common/core/src/main/java/is/codion/common/event/DefaultObserver.java
+++ b/common/core/src/main/java/is/codion/common/event/DefaultObserver.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.observer.Observer;
 
+import org.jspecify.annotations.Nullable;
+
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.LinkedHashSet;
@@ -34,10 +36,10 @@ final class DefaultObserver<T> implements Observer<T> {
 
 	private final Object lock = new Object();
 
-	private Set<Runnable> listeners;
-	private Set<Consumer<? super T>> consumers;
-	private List<WeakReference<Runnable>> weakListeners;
-	private List<WeakReference<Consumer<? super T>>> weakConsumers;
+	private @Nullable Set<Runnable> listeners;
+	private @Nullable Set<Consumer<? super T>> consumers;
+	private @Nullable List<WeakReference<Runnable>> weakListeners;
+	private @Nullable List<WeakReference<Consumer<? super T>>> weakConsumers;
 
 	@Override
 	public boolean addConsumer(Consumer<? super T> consumer) {
@@ -121,7 +123,7 @@ public boolean removeWeakConsumer(Consumer<? super T> consumer) {
 		}
 	}
 
-	void notifyListeners(T data) {
+	void notifyListeners(@Nullable T data) {
 		for (Runnable listener : listeners()) {
 			listener.run();
 		}
diff --git a/common/core/src/main/java/is/codion/common/event/Event.java b/common/core/src/main/java/is/codion/common/event/Event.java
index 2b476c95b6..30435a9d03 100644
--- a/common/core/src/main/java/is/codion/common/event/Event.java
+++ b/common/core/src/main/java/is/codion/common/event/Event.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.observer.Observer;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Consumer;
 
 /**
@@ -79,7 +81,7 @@ public interface Event<T> extends Runnable, Consumer<T>, Observer<T> {
 	 * @param data data associated with the event
 	 */
 	@Override
-	void accept(T data);
+	void accept(@Nullable T data);
 
 	/**
 	 * @return an observer notified each time this event occurs
diff --git a/common/core/src/main/java/is/codion/common/event/package-info.java b/common/core/src/main/java/is/codion/common/event/package-info.java
new file mode 100644
index 0000000000..d154990599
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/event/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Event related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.event;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/format/DefaultLocaleDateTimePattern.java b/common/core/src/main/java/is/codion/common/format/DefaultLocaleDateTimePattern.java
index d6d57fed56..1072003f0e 100644
--- a/common/core/src/main/java/is/codion/common/format/DefaultLocaleDateTimePattern.java
+++ b/common/core/src/main/java/is/codion/common/format/DefaultLocaleDateTimePattern.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.format;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 import java.time.chrono.IsoChronology;
@@ -49,7 +51,7 @@ final class DefaultLocaleDateTimePattern implements LocaleDateTimePattern, Seria
 
 	private final String delimiter;
 	private final boolean fourDigitYear;
-	private final String timePattern;
+	private final @Nullable String timePattern;
 
 	private DefaultLocaleDateTimePattern(DefaultBuilder builder) {
 		this.delimiter = requireNonNull(builder.delimiter, "delimiter must be specified");
@@ -92,7 +94,7 @@ private static String datePattern(Locale locale, String delimiter, boolean fourD
 	}
 
 	private static String dateTimePattern(Locale locale, String delimiter, boolean fourDigitYear,
-																				String timePattern) {
+																				@Nullable String timePattern) {
 		requireNonNull(locale);
 		String datePattern = DateTimeFormatterBuilder.
 						getLocalizedDateTimePattern(FormatStyle.SHORT, null, IsoChronology.INSTANCE, locale).toLowerCase(locale);
@@ -142,7 +144,7 @@ static final class DefaultBuilder implements Builder {
 
 		private String delimiter = ".";
 		private boolean fourDigitYear = true;
-		private String timePattern;
+		private @Nullable String timePattern;
 
 		@Override
 		public Builder delimiter(String delimiter) {
diff --git a/common/core/src/main/java/is/codion/common/format/package-info.java b/common/core/src/main/java/is/codion/common/format/package-info.java
new file mode 100644
index 0000000000..148f7b0abe
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/format/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Formatting related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.format;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/item/AbstractItem.java b/common/core/src/main/java/is/codion/common/item/AbstractItem.java
index db77681025..8e15323593 100644
--- a/common/core/src/main/java/is/codion/common/item/AbstractItem.java
+++ b/common/core/src/main/java/is/codion/common/item/AbstractItem.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.item;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 import java.util.Objects;
@@ -27,18 +29,18 @@ abstract class AbstractItem<T> implements Item<T>, Serializable {
 	@Serial
 	private static final long serialVersionUID = 1;
 
-	private final T value;
+	private final @Nullable T value;
 
 	/**
 	 * Creates a new Item.
 	 * @param value the value, may be null
 	 */
-	AbstractItem(T value) {
+	AbstractItem(@Nullable T value) {
 		this.value = value;
 	}
 
 	@Override
-	public final T value() {
+	public final @Nullable T value() {
 		return value;
 	}
 
diff --git a/common/core/src/main/java/is/codion/common/item/DefaultItem.java b/common/core/src/main/java/is/codion/common/item/DefaultItem.java
index be6e50ae7c..d9f79e0387 100644
--- a/common/core/src/main/java/is/codion/common/item/DefaultItem.java
+++ b/common/core/src/main/java/is/codion/common/item/DefaultItem.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.item;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 
@@ -32,7 +34,7 @@ final class DefaultItem<T> extends AbstractItem<T> implements Serializable {
 
 	private final String caption;
 
-	DefaultItem(T value, String caption) {
+	DefaultItem(@Nullable T value, String caption) {
 		super(value);
 		this.caption = requireNonNull(caption, "Item caption may not be null");
 	}
diff --git a/common/core/src/main/java/is/codion/common/item/Item.java b/common/core/src/main/java/is/codion/common/item/Item.java
index 47dd6a0457..7f11909f27 100644
--- a/common/core/src/main/java/is/codion/common/item/Item.java
+++ b/common/core/src/main/java/is/codion/common/item/Item.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.item;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * A class encapsulating a constant value and a caption representing the value.
  * {@link Item}s equality is based on their values only.
@@ -38,7 +40,7 @@ public interface Item<T> {
 	/**
 	 * @return the item value
 	 */
-	T value();
+	@Nullable T value();
 
 	/**
 	 * Returns an {@link Item}, with the caption as item.toString() or an empty string in case of a null value
@@ -46,7 +48,7 @@ public interface Item<T> {
 	 * @param <T> the value type
 	 * @return an {@link Item} based on the given value
 	 */
-	static <T> Item<T> item(T value) {
+	static <T> Item<T> item(@Nullable T value) {
 		if (value == null) {
 			return (Item<T>) DefaultItem.NULL_ITEM;
 		}
@@ -62,7 +64,7 @@ static <T> Item<T> item(T value) {
 	 * @return an {@link Item} based on the given value and caption
 	 * @throws NullPointerException if caption is null
 	 */
-	static <T> Item<T> item(T value, String caption) {
+	static <T> Item<T> item(@Nullable T value, String caption) {
 		return new DefaultItem<>(value, caption);
 	}
 
@@ -76,7 +78,7 @@ static <T> Item<T> item(T value, String caption) {
 	 * @param <T> the value type
 	 * @return an Item based on the given value and resource bundle
 	 */
-	static <T> Item<T> itemI18n(T value, String resourceBundleName, String resourceBundleKey) {
+	static <T> Item<T> itemI18n(@Nullable T value, String resourceBundleName, String resourceBundleKey) {
 		return new ItemI18n<>(value, resourceBundleName, resourceBundleKey);
 	}
 }
diff --git a/common/core/src/main/java/is/codion/common/item/ItemI18n.java b/common/core/src/main/java/is/codion/common/item/ItemI18n.java
index 80a5f2c79b..028bb33e5a 100644
--- a/common/core/src/main/java/is/codion/common/item/ItemI18n.java
+++ b/common/core/src/main/java/is/codion/common/item/ItemI18n.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.item;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 
@@ -32,9 +34,9 @@ final class ItemI18n<T> extends AbstractItem<T> implements Serializable {
 	private final String resourceBundleName;
 	private final String resourceBundleKey;
 
-	private transient String caption;
+	private transient @Nullable String caption;
 
-	ItemI18n(T value, String resourceBundleName, String resourceBundleKey) {
+	ItemI18n(@Nullable T value, String resourceBundleName, String resourceBundleKey) {
 		super(value);
 		getBundle(requireNonNull(resourceBundleName)).getString(requireNonNull(resourceBundleKey));
 		this.resourceBundleName = resourceBundleName;
diff --git a/common/core/src/main/java/is/codion/common/item/package-info.java b/common/core/src/main/java/is/codion/common/item/package-info.java
new file mode 100644
index 0000000000..356d8a8892
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/item/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>See {@link is.codion.common.item.Item}.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.item;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/logging/DefaultMethodLogger.java b/common/core/src/main/java/is/codion/common/logging/DefaultMethodLogger.java
index 29420798bd..a01b1a44c9 100644
--- a/common/core/src/main/java/is/codion/common/logging/DefaultMethodLogger.java
+++ b/common/core/src/main/java/is/codion/common/logging/DefaultMethodLogger.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.Text;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.PrintWriter;
 import java.io.Serial;
 import java.io.Serializable;
@@ -71,17 +73,17 @@ public synchronized void enter(String method, Object argument) {
 	}
 
 	@Override
-	public Entry exit(String method) {
+	public @Nullable Entry exit(String method) {
 		return exit(method, null);
 	}
 
 	@Override
-	public Entry exit(String method, Exception exception) {
+	public @Nullable Entry exit(String method, @Nullable Exception exception) {
 		return exit(method, exception, null);
 	}
 
 	@Override
-	public synchronized Entry exit(String method, Exception exception, String exitMessage) {
+	public synchronized @Nullable Entry exit(String method, @Nullable Exception exception, @Nullable String exitMessage) {
 		if (!enabled) {
 			return null;
 		}
@@ -141,20 +143,20 @@ private static final class DefaultEntry implements Entry, Serializable {
 
 		private final LinkedList<Entry> childEntries = new LinkedList<>();
 		private final String method;
-		private final String enterMessage;
+		private final @Nullable String enterMessage;
 		private final long enterTime;
 		private final long enterTimeNano;
-		private String exitMessage;
+		private @Nullable String exitMessage;
 		private long exitTime;
 		private long exitTimeNano;
-		private String stackTrace;
+		private @Nullable String stackTrace;
 
 		/**
 		 * Creates a new Entry, using the current time
 		 * @param method the method being logged
 		 * @param enterMessage the message associated with entering the method
 		 */
-		private DefaultEntry(String method, String enterMessage) {
+		private DefaultEntry(String method, @Nullable String enterMessage) {
 			this(method, enterMessage, currentTimeMillis(), nanoTime());
 		}
 
@@ -165,8 +167,8 @@ private DefaultEntry(String method, String enterMessage) {
 		 * @param enterTime the time to associate with entering the method
 		 * @param enterTimeNano the nano time to associate with entering the method
 		 */
-		private DefaultEntry(String method, String enterMessage, long enterTime, long enterTimeNano) {
-			this.method = method;
+		private DefaultEntry(String method, @Nullable String enterMessage, long enterTime, long enterTimeNano) {
+			this.method = requireNonNull(method);
 			this.enterTime = enterTime;
 			this.enterTimeNano = enterTimeNano;
 			this.enterMessage = enterMessage;
@@ -183,7 +185,7 @@ public String method() {
 		}
 
 		@Override
-		public String enterMessage() {
+		public @Nullable String enterMessage() {
 			return enterMessage;
 		}
 
@@ -243,7 +245,7 @@ private void setExitTime() {
 		/**
 		 * @param exception the exception that occurred during the method call logged by this entry
 		 */
-		private void setException(Exception exception) {
+		private void setException(@Nullable Exception exception) {
 			if (exception != null) {
 				stackTrace = stackTrace(exception);
 			}
@@ -252,7 +254,7 @@ private void setException(Exception exception) {
 		/**
 		 * @param exitMessage the exit message
 		 */
-		private void setExitMessage(String exitMessage) {
+		private void setExitMessage(@Nullable String exitMessage) {
 			this.exitMessage = exitMessage;
 		}
 
diff --git a/common/core/src/main/java/is/codion/common/logging/MethodLogger.java b/common/core/src/main/java/is/codion/common/logging/MethodLogger.java
index 22e4b6b136..2fe50447b3 100644
--- a/common/core/src/main/java/is/codion/common/logging/MethodLogger.java
+++ b/common/core/src/main/java/is/codion/common/logging/MethodLogger.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.logging;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Collection;
 import java.util.List;
 
@@ -46,14 +48,14 @@ public interface MethodLogger {
 	 * @param method the method being exited
 	 * @return the Entry
 	 */
-	Entry exit(String method);
+	@Nullable Entry exit(String method);
 
 	/**
 	 * @param method the method being exited
 	 * @param exception the exception, if any
 	 * @return the Entry
 	 */
-	Entry exit(String method, Exception exception);
+	@Nullable Entry exit(String method, @Nullable Exception exception);
 
 	/**
 	 * @param method the method being exited
@@ -61,7 +63,7 @@ public interface MethodLogger {
 	 * @param exitMessage the message to associate with exiting the method
 	 * @return the Entry, or null if this logger is not enabled
 	 */
-	Entry exit(String method, Exception exception, String exitMessage);
+	@Nullable Entry exit(String method, @Nullable Exception exception, @Nullable String exitMessage);
 
 	/**
 	 * @return true if this logger is enabled
@@ -115,7 +117,7 @@ interface Entry {
 		/**
 		 * @return the entry message
 		 */
-		String enterMessage();
+		@Nullable String enterMessage();
 
 		/**
 		 * Returns the duration of the method call this entry represents in nanoseconds,
diff --git a/common/core/src/main/java/is/codion/common/logging/package-info.java b/common/core/src/main/java/is/codion/common/logging/package-info.java
new file mode 100644
index 0000000000..eda54870da
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/logging/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Logging related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.logging;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/observer/Mutable.java b/common/core/src/main/java/is/codion/common/observer/Mutable.java
index f6ac7b4110..245eff5a92 100644
--- a/common/core/src/main/java/is/codion/common/observer/Mutable.java
+++ b/common/core/src/main/java/is/codion/common/observer/Mutable.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.observer;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * A wrapper for a mutable value, providing a change observer.
  * <pre>
@@ -68,7 +70,7 @@ public interface Mutable<T> extends Observable<T> {
 	 * Sets the value
 	 * @param value the value to set
 	 */
-	void set(T value);
+	void set(@Nullable T value);
 
 	/**
 	 * Clears this {@link Mutable} instance by setting the value to null
diff --git a/common/core/src/main/java/is/codion/common/observer/Observable.java b/common/core/src/main/java/is/codion/common/observer/Observable.java
index 445b8079f5..4495bb7b84 100644
--- a/common/core/src/main/java/is/codion/common/observer/Observable.java
+++ b/common/core/src/main/java/is/codion/common/observer/Observable.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.observer;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Optional;
 import java.util.function.Consumer;
 
@@ -65,7 +67,7 @@ public interface Observable<T> extends Observer<T> {
 	/**
 	 * @return the value
 	 */
-	T get();
+	@Nullable T get();
 
 	/**
 	 * @return an Optional based on the current value
diff --git a/common/core/src/main/java/is/codion/common/observer/package-info.java b/common/core/src/main/java/is/codion/common/observer/package-info.java
new file mode 100644
index 0000000000..6ec87818be
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/observer/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>{@link is.codion.common.observer.Observer}, {@link is.codion.common.observer.Observable} and {@link is.codion.common.observer.Mutable}.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.observer;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/package-info.java b/common/core/src/main/java/is/codion/common/package-info.java
index 701349218e..83091b2ad8 100644
--- a/common/core/src/main/java/is/codion/common/package-info.java
+++ b/common/core/src/main/java/is/codion/common/package-info.java
@@ -17,9 +17,11 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>Common classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.Text#DEFAULT_COLLATOR_LANGUAGE}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/property/DefaultPropertyStore.java b/common/core/src/main/java/is/codion/common/property/DefaultPropertyStore.java
index 46fe36c0ec..9769af428a 100644
--- a/common/core/src/main/java/is/codion/common/property/DefaultPropertyStore.java
+++ b/common/core/src/main/java/is/codion/common/property/DefaultPropertyStore.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.value.AbstractValue;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
@@ -132,7 +134,7 @@ public PropertyValue<Character> characterValue(String propertyName, char default
 
 	@Override
 	public PropertyValue<String> stringValue(String propertyName) {
-		return stringValue(propertyName, null);
+		return value(propertyName, Objects::toString, Objects::toString);
 	}
 
 	@Override
@@ -142,7 +144,9 @@ public PropertyValue<String> stringValue(String propertyName, String defaultValu
 
 	@Override
 	public <T extends Enum<T>> PropertyValue<T> enumValue(String propertyName, Class<T> enumClass) {
-		return enumValue(propertyName, enumClass, null);
+		requireNonNull(enumClass);
+
+		return value(propertyName, value -> Enum.valueOf(enumClass, value.toUpperCase()), Objects::toString);
 	}
 
 	@Override
@@ -154,7 +158,7 @@ public <T extends Enum<T>> PropertyValue<T> enumValue(String propertyName, Class
 
 	@Override
 	public <T> PropertyValue<List<T>> listValue(String propertyName, Function<String, T> decoder, Function<T, String> encoder) {
-		return listValue(propertyName, decoder, encoder, emptyList());
+		return value(propertyName, new ListValueDecoder<>(decoder), new ListValueEncoder<>(encoder), emptyList());
 	}
 
 	@Override
@@ -164,7 +168,13 @@ public <T> PropertyValue<List<T>> listValue(String propertyName, Function<String
 
 	@Override
 	public <T> PropertyValue<T> value(String propertyName, Function<String, T> decoder, Function<T, String> encoder) {
-		return value(propertyName, decoder, encoder, null);
+		if (propertyValues.containsKey(requireNonNull(propertyName))) {
+			throw new IllegalStateException("A value has already been created for the property '" + propertyName + "'");
+		}
+		DefaultPropertyValue<T> value = new DefaultPropertyValue<>(propertyName, decoder, encoder);
+		propertyValues.put(propertyName, value);
+
+		return value;
 	}
 
 	@Override
@@ -184,7 +194,7 @@ public <T> Optional<PropertyValue<T>> propertyValue(String propertyName) {
 	}
 
 	@Override
-	public void setProperty(String propertyName, String value) {
+	public void setProperty(String propertyName, @Nullable String value) {
 		if (propertyValues.containsKey(requireNonNull(propertyName))) {
 			throw new IllegalArgumentException("Value bound properties can only be modified through their Value instances");
 		}
@@ -273,10 +283,17 @@ private final class DefaultPropertyValue<T> extends AbstractValue<T> implements
 		private final String propertyName;
 		private final Function<T, String> encoder;
 
-		private T value;
+		private @Nullable T value;
+
+		private DefaultPropertyValue(String propertyName, Function<String, T> decoder, Function<T, String> encoder) {
+			super(null, Notify.WHEN_CHANGED);
+			this.propertyName = requireNonNull(propertyName);
+			this.encoder = requireNonNull(encoder);
+			set(getInitialValue(propertyName, requireNonNull(decoder)));
+		}
 
 		private DefaultPropertyValue(String propertyName, Function<String, T> decoder, Function<T, String> encoder, T defaultValue) {
-			super(defaultValue, Notify.WHEN_CHANGED);
+			super(requireNonNull(defaultValue), Notify.WHEN_CHANGED);
 			this.propertyName = requireNonNull(propertyName);
 			this.encoder = requireNonNull(encoder);
 			set(getInitialValue(propertyName, requireNonNull(decoder)));
@@ -307,12 +324,12 @@ public String toString() {
 		}
 
 		@Override
-		protected T getValue() {
+		protected @Nullable T getValue() {
 			return value;
 		}
 
 		@Override
-		protected void setValue(T value) {
+		protected void setValue(@Nullable T value) {
 			this.value = value;
 			if (value == null) {
 				properties.remove(propertyName);
@@ -324,7 +341,7 @@ protected void setValue(T value) {
 			}
 		}
 
-		private T getInitialValue(String property, Function<String, T> decoder) {
+		private @Nullable T getInitialValue(String property, Function<String, T> decoder) {
 			String initialValue = System.getProperty(property);
 			if (initialValue == null) {
 				initialValue = properties.getProperty(property);
@@ -343,7 +360,7 @@ private ListValueDecoder(Function<String, T> decoder) {
 		}
 
 		@Override
-		public List<T> apply(String stringValue) {
+		public List<T> apply(@Nullable String stringValue) {
 			return stringValue == null ? emptyList() : Arrays.stream(stringValue.split(VALUE_SEPARATOR))
 							.map(decoder)
 							.collect(toList());
diff --git a/common/core/src/main/java/is/codion/common/property/PropertyStore.java b/common/core/src/main/java/is/codion/common/property/PropertyStore.java
index 057df68467..8685b098fc 100644
--- a/common/core/src/main/java/is/codion/common/property/PropertyStore.java
+++ b/common/core/src/main/java/is/codion/common/property/PropertyStore.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.property.DefaultPropertyStore.DefaultSystemPropertyFormatter;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
@@ -249,7 +251,7 @@ public interface PropertyStore {
 	 * @param value the value
 	 * @throws IllegalArgumentException if the property is value bound
 	 */
-	void setProperty(String propertyName, String value);
+	void setProperty(String propertyName, @Nullable String value);
 
 	/**
 	 * Retrieves the value for the given property, null if no value is present
diff --git a/common/core/src/main/java/is/codion/common/property/package-info.java b/common/core/src/main/java/is/codion/common/property/package-info.java
new file mode 100644
index 0000000000..df4f4cd397
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/property/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Propery related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.property;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/proxy/DefaultProxyBuilder.java b/common/core/src/main/java/is/codion/common/proxy/DefaultProxyBuilder.java
index 1e2113392f..09644a4d2e 100644
--- a/common/core/src/main/java/is/codion/common/proxy/DefaultProxyBuilder.java
+++ b/common/core/src/main/java/is/codion/common/proxy/DefaultProxyBuilder.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.proxy;
 
+import org.jspecify.annotations.Nullable;
+
 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
@@ -38,7 +40,7 @@ final class DefaultProxyBuilder<T> implements ProxyBuilder<T> {
 	private final Map<MethodKey, ProxyMethod<T>> methodMap = new HashMap<>();
 	private final Class<T> interfaceToProxy;
 
-	private T delegate;
+	private @Nullable T delegate;
 
 	DefaultProxyBuilder(Class<T> interfaceToProxy) {
 		if (!requireNonNull(interfaceToProxy).isInterface()) {
@@ -119,15 +121,15 @@ private static final class DefaultHandler<T> implements InvocationHandler {
 		private static final String EQUALS = "equals";
 
 		private final Map<MethodKey, ProxyMethod<T>> methodMap;
-		private final T delegate;
+		private final @Nullable T delegate;
 
-		private DefaultHandler(Map<MethodKey, ProxyMethod<T>> methodMap, T delegate) {
+		private DefaultHandler(Map<MethodKey, ProxyMethod<T>> methodMap, @Nullable T delegate) {
 			this.methodMap = methodMap;
 			this.delegate = delegate;
 		}
 
 		@Override
-		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+		public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable {
 			ProxyMethod<T> proxyMethod = methodMap.get(new MethodKey(method));
 			if (proxyMethod != null) {
 				return proxyMethod.invoke(new DefaultProxyMethodParameters<>((T) proxy, delegate, args));
@@ -157,10 +159,10 @@ private static boolean isEqualsMethod(Method method) {
 	private static final class DefaultProxyMethodParameters<T> implements ProxyMethod.Parameters<T> {
 
 		private final T proxy;
-		private final T delegate;
+		private final @Nullable T delegate;
 		private final List<?> arguments;
 
-		private DefaultProxyMethodParameters(T proxy, T delegate, Object[] arguments) {
+		private DefaultProxyMethodParameters(T proxy, @Nullable T delegate, @Nullable Object[] arguments) {
 			this.proxy = requireNonNull(proxy);
 			this.delegate = delegate;
 			this.arguments = arguments == null ? emptyList() : unmodifiableList(Arrays.asList(arguments));
diff --git a/common/core/src/main/java/is/codion/common/proxy/ProxyBuilder.java b/common/core/src/main/java/is/codion/common/proxy/ProxyBuilder.java
index 50b3ed4198..a949168552 100644
--- a/common/core/src/main/java/is/codion/common/proxy/ProxyBuilder.java
+++ b/common/core/src/main/java/is/codion/common/proxy/ProxyBuilder.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.proxy;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.List;
 
 /**
@@ -109,10 +111,10 @@ interface ProxyMethod<T> {
 		/**
 		 * Invokes this proxy method.
 		 * @param parameters the parameters
-		 * @return the result
+		 * @return the result, may be null
 		 * @throws Throwable in case of an exception
 		 */
-		Object invoke(Parameters<T> parameters) throws Throwable;
+		@Nullable Object invoke(Parameters<T> parameters) throws Throwable;
 
 		/**
 		 * Parameters available to the invocation handler when calling a proxy method.
diff --git a/common/core/src/main/java/is/codion/common/proxy/package-info.java b/common/core/src/main/java/is/codion/common/proxy/package-info.java
new file mode 100644
index 0000000000..81905fc653
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/proxy/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Dynamic proxy related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.proxy;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/resource/package-info.java b/common/core/src/main/java/is/codion/common/resource/package-info.java
new file mode 100644
index 0000000000..02ae140d87
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/resource/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Resource bundle related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.resource;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/scheduler/DefaultTaskScheduler.java b/common/core/src/main/java/is/codion/common/scheduler/DefaultTaskScheduler.java
index 2c39816d27..5b733627a4 100644
--- a/common/core/src/main/java/is/codion/common/scheduler/DefaultTaskScheduler.java
+++ b/common/core/src/main/java/is/codion/common/scheduler/DefaultTaskScheduler.java
@@ -21,6 +21,8 @@
 import is.codion.common.value.Value;
 import is.codion.common.value.Value.Validator;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ThreadFactory;
@@ -39,7 +41,7 @@ final class DefaultTaskScheduler implements TaskScheduler {
 	private final TimeUnit timeUnit;
 	private final ThreadFactory threadFactory;
 
-	private ScheduledExecutorService executorService;
+	private @Nullable ScheduledExecutorService executorService;
 
 	private DefaultTaskScheduler(DefaultBuilder builder) {
 		this.task = builder.task;
@@ -68,7 +70,7 @@ public DefaultTaskScheduler start() {
 		synchronized (lock) {
 			stop();
 			executorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
-			executorService.scheduleAtFixedRate(task, initialDelay, interval.get(), timeUnit);
+			executorService.scheduleAtFixedRate(task, initialDelay, interval.getOrThrow(), timeUnit);
 
 			return this;
 		}
@@ -77,7 +79,7 @@ public DefaultTaskScheduler start() {
 	@Override
 	public void stop() {
 		synchronized (lock) {
-			if (running()) {
+			if (running() && executorService != null) {
 				executorService.shutdownNow();
 				executorService = null;
 			}
@@ -105,7 +107,7 @@ static final class DefaultBuilder implements Builder {
 
 		private int interval;
 		private int initialDelay;
-		private TimeUnit timeUnit;
+		private @Nullable TimeUnit timeUnit;
 		private ThreadFactory threadFactory = new DaemonThreadFactory();
 
 		DefaultBuilder(Runnable task) {
diff --git a/common/core/src/main/java/is/codion/common/scheduler/package-info.java b/common/core/src/main/java/is/codion/common/scheduler/package-info.java
new file mode 100644
index 0000000000..4e305caf88
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/scheduler/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Task scheduling related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.scheduler;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/state/DefaultState.java b/common/core/src/main/java/is/codion/common/state/DefaultState.java
index 004706c4fb..665da57f88 100644
--- a/common/core/src/main/java/is/codion/common/state/DefaultState.java
+++ b/common/core/src/main/java/is/codion/common/state/DefaultState.java
@@ -21,6 +21,8 @@
 import is.codion.common.value.Value;
 import is.codion.common.value.ValueObserver;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -28,7 +30,7 @@ final class DefaultState implements State {
 
 	private final Value<Boolean> value;
 
-	private DefaultStateObserver observer;
+	private @Nullable DefaultStateObserver observer;
 
 	private DefaultState(Value.Builder<Boolean, ?> valueBuilder) {
 		this.value = valueBuilder.consumer(new Notifier()).build();
@@ -36,18 +38,18 @@ private DefaultState(Value.Builder<Boolean, ?> valueBuilder) {
 
 	@Override
 	public String toString() {
-		return Boolean.toString(value.get());
+		return Boolean.toString(value.getOrThrow());
 	}
 
 	@Override
 	public Boolean get() {
 		synchronized (this.value) {
-			return this.value.get();
+			return this.value.getOrThrow();
 		}
 	}
 
 	@Override
-	public boolean set(Boolean value) {
+	public boolean set(@Nullable Boolean value) {
 		synchronized (this.value) {
 			return this.value.set(value);
 		}
@@ -193,7 +195,7 @@ static final class DefaultBuilder implements Builder {
 		}
 
 		@Override
-		public Builder value(Boolean value) {
+		public Builder value(@Nullable Boolean value) {
 			valueBuilder.value(value);
 			return this;
 		}
diff --git a/common/core/src/main/java/is/codion/common/state/DefaultStateCombination.java b/common/core/src/main/java/is/codion/common/state/DefaultStateCombination.java
index 720d7880e7..70e549ec6c 100644
--- a/common/core/src/main/java/is/codion/common/state/DefaultStateCombination.java
+++ b/common/core/src/main/java/is/codion/common/state/DefaultStateCombination.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.Conjunction;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -158,7 +160,7 @@ public boolean removeWeakConsumer(Consumer<? super Boolean> consumer) {
 		return observer.removeWeakConsumer(consumer);
 	}
 
-	private boolean get(Conjunction conjunction, StateObserver exclude, boolean excludeReplacement) {
+	private boolean get(Conjunction conjunction, @Nullable StateObserver exclude, boolean excludeReplacement) {
 		for (StateCombinationConsumer listener : stateListeners) {
 			StateObserver state = listener.state;
 			boolean value = state.equals(exclude) ? excludeReplacement : state.get();
diff --git a/common/core/src/main/java/is/codion/common/state/DefaultStateGroup.java b/common/core/src/main/java/is/codion/common/state/DefaultStateGroup.java
index cceb50c31f..1e81d3d0bd 100644
--- a/common/core/src/main/java/is/codion/common/state/DefaultStateGroup.java
+++ b/common/core/src/main/java/is/codion/common/state/DefaultStateGroup.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.value.ValueObserver;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -31,7 +33,7 @@ final class DefaultStateGroup implements State.Group {
 
 	private final List<State> members = new ArrayList<>();
 
-	private State previousState;
+	private @Nullable State previousState;
 	private boolean disablingStates = false;
 
 	DefaultStateGroup(State... states) {
@@ -98,7 +100,7 @@ else if (members.size() > 1) {
 		previousState = current;
 	}
 
-	private State previousState(State current) {
+	private @Nullable State previousState(State current) {
 		return members.stream()
 						.filter(state -> state != current)
 						.filter(ValueObserver::get)
diff --git a/common/core/src/main/java/is/codion/common/state/DefaultStateObserver.java b/common/core/src/main/java/is/codion/common/state/DefaultStateObserver.java
index 669b3c4eeb..aa1e5016db 100644
--- a/common/core/src/main/java/is/codion/common/state/DefaultStateObserver.java
+++ b/common/core/src/main/java/is/codion/common/state/DefaultStateObserver.java
@@ -21,6 +21,8 @@
 import is.codion.common.event.Event;
 import is.codion.common.observer.Observer;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Consumer;
 
 import static java.util.Objects.requireNonNull;
@@ -31,8 +33,8 @@ final class DefaultStateObserver implements StateObserver {
 	private final StateObserver observedState;
 	private final boolean not;
 
-	private Event<Boolean> stateChangedEvent;
-	private DefaultStateObserver notObserver;
+	private @Nullable Event<Boolean> stateChangedEvent;
+	private @Nullable DefaultStateObserver notObserver;
 
 	DefaultStateObserver(StateObserver observedState, boolean not) {
 		this.observedState = requireNonNull(observedState);
diff --git a/common/core/src/main/java/is/codion/common/state/State.java b/common/core/src/main/java/is/codion/common/state/State.java
index f176026a26..3a3f0ea3cf 100644
--- a/common/core/src/main/java/is/codion/common/state/State.java
+++ b/common/core/src/main/java/is/codion/common/state/State.java
@@ -21,6 +21,8 @@
 import is.codion.common.Conjunction;
 import is.codion.common.value.Value;
 
+import org.jspecify.annotations.NonNull;
+
 import java.util.Collection;
 
 /**
@@ -44,6 +46,9 @@
  */
 public interface State extends StateObserver, Value<Boolean> {
 
+	@Override
+	@NonNull Boolean get();
+
 	/**
 	 * Returns a {@link StateObserver} notified each time the state changes
 	 * @return a {@link StateObserver} notified each time the state changes
diff --git a/common/core/src/main/java/is/codion/common/state/StateObserver.java b/common/core/src/main/java/is/codion/common/state/StateObserver.java
index 55511e7779..e93f486d5a 100644
--- a/common/core/src/main/java/is/codion/common/state/StateObserver.java
+++ b/common/core/src/main/java/is/codion/common/state/StateObserver.java
@@ -20,11 +20,16 @@
 
 import is.codion.common.value.ValueObserver;
 
+import org.jspecify.annotations.NonNull;
+
 /**
  * Specifies an observer for a {@link State} instance.
  */
 public interface StateObserver extends ValueObserver<Boolean> {
 
+	@Override
+	@NonNull Boolean get();
+
 	/**
 	 * @return false
 	 */
diff --git a/common/core/src/main/java/is/codion/common/state/package-info.java b/common/core/src/main/java/is/codion/common/state/package-info.java
new file mode 100644
index 0000000000..4722eabb7e
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/state/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>See {@link is.codion.common.state.State} and {@link is.codion.common.state.StateObserver}.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.state;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/user/DefaultUser.java b/common/core/src/main/java/is/codion/common/user/DefaultUser.java
index f4651ed01c..568d56cad3 100644
--- a/common/core/src/main/java/is/codion/common/user/DefaultUser.java
+++ b/common/core/src/main/java/is/codion/common/user/DefaultUser.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.user;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
@@ -35,7 +37,7 @@ final class DefaultUser implements User, Serializable {
 	private String username;
 	private char[] password;
 
-	DefaultUser(String username, char[] password) {
+	DefaultUser(String username, char @Nullable[] password) {
 		if (requireNonNull(username).isEmpty()) {
 			throw new IllegalArgumentException("Username must be non-empty");
 		}
@@ -95,7 +97,7 @@ private void readObject(ObjectInputStream stream) throws IOException, ClassNotFo
 		this.password = createPassword((char[]) stream.readObject());
 	}
 
-	private static char[] createPassword(char[] password) {
+	private static char[] createPassword(char @Nullable[] password) {
 		return password == null ? new char[0] : Arrays.copyOf(password, password.length);
 	}
 }
diff --git a/common/core/src/main/java/is/codion/common/user/User.java b/common/core/src/main/java/is/codion/common/user/User.java
index 30cd71adaa..9489f82d20 100644
--- a/common/core/src/main/java/is/codion/common/user/User.java
+++ b/common/core/src/main/java/is/codion/common/user/User.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.user;
 
+import org.jspecify.annotations.Nullable;
+
 import static java.util.Objects.requireNonNull;
 
 /**
@@ -68,7 +70,7 @@ static User user(String username) {
 	 * @return a new User
 	 * @throws IllegalArgumentException in case username is an empty string
 	 */
-	static User user(String username, char[] password) {
+	static User user(String username, char @Nullable[] password) {
 		return new DefaultUser(username, password);
 	}
 
diff --git a/common/core/src/main/java/is/codion/common/user/package-info.java b/common/core/src/main/java/is/codion/common/user/package-info.java
new file mode 100644
index 0000000000..b7ee81ea5c
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/user/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>See {@link is.codion.common.user.User}.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.user;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/value/AbstractValue.java b/common/core/src/main/java/is/codion/common/value/AbstractValue.java
index df5817e136..2c4fdb82a5 100644
--- a/common/core/src/main/java/is/codion/common/value/AbstractValue.java
+++ b/common/core/src/main/java/is/codion/common/value/AbstractValue.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.event.Event;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
@@ -46,14 +48,14 @@
  */
 public abstract class AbstractValue<T> implements Value<T> {
 
-	private final T nullValue;
-	private final Notify notify;
+	private final @Nullable T nullValue;
+	private final @Nullable Notify notify;
 
-	private Event<T> notifier;
-	private Set<Validator<? super T>> validators;
-	private Map<Value<T>, ValueLink<T>> linkedValues;
-	private Map<ValueObserver<T>, ValueObserverLink> linkedObservers;
-	private ValueObserver<T> observer;
+	private @Nullable Event<T> notifier;
+	private @Nullable Set<Validator<? super T>> validators;
+	private @Nullable Map<Value<T>, ValueLink<T>> linkedValues;
+	private @Nullable Map<ValueObserver<T>, ValueObserverLink> linkedObservers;
+	private @Nullable ValueObserver<T> observer;
 
 	/**
 	 * Creates a {@link AbstractValue} instance, which does not notify listeners.
@@ -66,7 +68,7 @@ protected AbstractValue() {
 	 * Creates a {@link AbstractValue} instance, which does not notify listeners.
 	 * @param nullValue the value to use instead of null
 	 */
-	protected AbstractValue(T nullValue) {
+	protected AbstractValue(@Nullable T nullValue) {
 		this.nullValue = nullValue;
 		this.notify = null;
 	}
@@ -76,18 +78,18 @@ protected AbstractValue(T nullValue) {
 	 * @param nullValue the value to use instead of null
 	 * @param notify specifies when to notify listeners
 	 */
-	protected AbstractValue(T nullValue, Notify notify) {
+	protected AbstractValue(@Nullable T nullValue, Notify notify) {
 		this.nullValue = nullValue;
 		this.notify = requireNonNull(notify);
 	}
 
 	@Override
-	public final T get() {
+	public final @Nullable T get() {
 		return getValue();
 	}
 
 	@Override
-	public final boolean set(T value) {
+	public final boolean set(@Nullable T value) {
 		T newValue = value == null ? nullValue : value;
 		for (Validator<? super T> validator : validators()) {
 			validator.validate(newValue);
@@ -123,7 +125,7 @@ public final boolean nullable() {
 	}
 
 	@Override
-	public final void accept(T data) {
+	public final void accept(@Nullable T data) {
 		set(data);
 	}
 
@@ -134,6 +136,7 @@ public final boolean addListener(Runnable listener) {
 
 	@Override
 	public final boolean removeListener(Runnable listener) {
+		requireNonNull(listener);
 		if (notifier != null) {
 			return notifier.removeListener(listener);
 		}
@@ -148,6 +151,7 @@ public final boolean addConsumer(Consumer<? super T> consumer) {
 
 	@Override
 	public final boolean removeConsumer(Consumer<? super T> consumer) {
+		requireNonNull(consumer);
 		if (notifier != null) {
 			return notifier.removeConsumer(consumer);
 		}
@@ -162,6 +166,7 @@ public final boolean addWeakListener(Runnable listener) {
 
 	@Override
 	public final boolean removeWeakListener(Runnable listener) {
+		requireNonNull(listener);
 		if (notifier != null) {
 			return notifier.removeWeakListener(listener);
 		}
@@ -176,6 +181,7 @@ public final boolean addWeakConsumer(Consumer<? super T> consumer) {
 
 	@Override
 	public final boolean removeWeakConsumer(Consumer<? super T> consumer) {
+		requireNonNull(consumer);
 		if (notifier != null) {
 			return notifier.removeWeakConsumer(consumer);
 		}
@@ -250,7 +256,7 @@ public final boolean removeValidator(Validator<? super T> validator) {
 	}
 
 	@Override
-	public final void validate(T value) {
+	public final void validate(@Nullable T value) {
 		validators().forEach(validator -> validator.validate(value));
 	}
 
@@ -258,13 +264,13 @@ public final void validate(T value) {
 	 * Returns the actual internal value.
 	 * @return the value
 	 */
-	protected abstract T getValue();
+	protected abstract @Nullable T getValue();
 
 	/**
 	 * Sets the actual internal value.
 	 * @param value the value
 	 */
-	protected abstract void setValue(T value);
+	protected abstract void setValue(@Nullable T value);
 
 	/**
 	 * Notifies listeners that the underlying value has changed or at least that it may have changed
diff --git a/common/core/src/main/java/is/codion/common/value/DefaultValue.java b/common/core/src/main/java/is/codion/common/value/DefaultValue.java
index 5cf2046b90..32ef8189f9 100644
--- a/common/core/src/main/java/is/codion/common/value/DefaultValue.java
+++ b/common/core/src/main/java/is/codion/common/value/DefaultValue.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
@@ -28,7 +30,7 @@ class DefaultValue<T> extends AbstractValue<T> {
 
 	protected final Object lock = new Object();
 
-	private T value;
+	private @Nullable T value;
 
 	protected DefaultValue(DefaultBuilder<T, ?> builder) {
 		super(builder.nullValue, builder.notify);
@@ -43,12 +45,12 @@ protected DefaultValue(DefaultBuilder<T, ?> builder) {
 	}
 
 	@Override
-	protected final T getValue() {
+	protected final @Nullable T getValue() {
 		return value;
 	}
 
 	@Override
-	protected final void setValue(T value) {
+	protected final void setValue(@Nullable T value) {
 		this.value = value;
 	}
 
@@ -65,7 +67,7 @@ static final class DefaultBuilderFactory implements BuilderFactory {
 		}
 
 		@Override
-		public <T> Builder<T, ?> nullable(T value) {
+		public <T> Builder<T, ?> nullable(@Nullable T value) {
 			return (Builder<T, ?>) new DefaultBuilder<>()
 							.value(value);
 		}
@@ -73,7 +75,7 @@ static final class DefaultBuilderFactory implements BuilderFactory {
 
 	static class DefaultBuilder<T, B extends Builder<T, B>> implements Builder<T, B> {
 
-		private final T nullValue;
+		private final @Nullable T nullValue;
 		private final List<Validator<? super T>> validators = new ArrayList<>();
 		private final List<Value<T>> linkedValues = new ArrayList<>();
 		private final List<ValueObserver<T>> linkedObservers = new ArrayList<>();
@@ -82,7 +84,7 @@ static class DefaultBuilder<T, B extends Builder<T, B>> implements Builder<T, B>
 		private final List<Consumer<? super T>> consumers = new ArrayList<>();
 		private final List<Consumer<? super T>> weakConsumers = new ArrayList<>();
 
-		private T value;
+		private @Nullable T value;
 		private Notify notify = Notify.WHEN_CHANGED;
 
 		DefaultBuilder() {
@@ -95,7 +97,7 @@ static class DefaultBuilder<T, B extends Builder<T, B>> implements Builder<T, B>
 		}
 
 		@Override
-		public final B value(T value) {
+		public final B value(@Nullable T value) {
 			this.value = value;
 			return self();
 		}
@@ -156,7 +158,7 @@ public Value<T> build() {
 		/**
 		 * @return the initial value
 		 */
-		protected T prepareInitialValue() {
+		protected @Nullable T prepareInitialValue() {
 			return value == null ? nullValue : value;
 		}
 
diff --git a/common/core/src/main/java/is/codion/common/value/DefaultValueObserver.java b/common/core/src/main/java/is/codion/common/value/DefaultValueObserver.java
index e738260e4d..25ab146964 100644
--- a/common/core/src/main/java/is/codion/common/value/DefaultValueObserver.java
+++ b/common/core/src/main/java/is/codion/common/value/DefaultValueObserver.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Consumer;
 
 import static java.util.Objects.requireNonNull;
@@ -31,7 +33,7 @@ class DefaultValueObserver<T> implements ValueObserver<T> {
 	}
 
 	@Override
-	public final T get() {
+	public final @Nullable T get() {
 		return value.get();
 	}
 
diff --git a/common/core/src/main/java/is/codion/common/value/DefaultValues.java b/common/core/src/main/java/is/codion/common/value/DefaultValues.java
index 09c839d36e..9e306fda29 100644
--- a/common/core/src/main/java/is/codion/common/value/DefaultValues.java
+++ b/common/core/src/main/java/is/codion/common/value/DefaultValues.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.function.Function;
@@ -34,7 +36,7 @@ class DefaultValues<T, C extends Collection<T>> extends DefaultValue<C>
 	private final Supplier<? extends C> create;
 	private final Function<C, C> unmodifiable;
 
-	private Value<T> singleValue;
+	private @Nullable Value<T> singleValue;
 
 	DefaultValues(DefaultBuilder<C, T, ?> builder) {
 		super(builder);
@@ -44,11 +46,11 @@ class DefaultValues<T, C extends Collection<T>> extends DefaultValue<C>
 
 	@Override
 	public final Iterator<T> iterator() {
-		return get().iterator();
+		return getOrThrow().iterator();
 	}
 
 	@Override
-	public final boolean set(Collection<T> values) {
+	public final boolean set(@Nullable Collection<T> values) {
 		synchronized (lock) {
 			C newValues = create.get();
 			if (values != null) {
@@ -60,10 +62,10 @@ public final boolean set(Collection<T> values) {
 	}
 
 	@Override
-	public final boolean add(T value) {
+	public final boolean add(@Nullable T value) {
 		synchronized (lock) {
 			C newValues = create.get();
-			newValues.addAll(get());
+			newValues.addAll(getOrThrow());
 			boolean added = newValues.add(value);
 			set(unmodifiable.apply(newValues));
 
@@ -81,7 +83,7 @@ public final boolean addAll(Collection<T> values) {
 		requireNonNull(values);
 		synchronized (lock) {
 			C newValues = create.get();
-			newValues.addAll(get());
+			newValues.addAll(getOrThrow());
 			boolean added = newValues.addAll(values);
 			set(unmodifiable.apply(newValues));
 
@@ -90,10 +92,10 @@ public final boolean addAll(Collection<T> values) {
 	}
 
 	@Override
-	public final boolean remove(T value) {
+	public final boolean remove(@Nullable T value) {
 		synchronized (lock) {
 			C newValues = create.get();
-			newValues.addAll(get());
+			newValues.addAll(getOrThrow());
 			boolean removed = newValues.remove(value);
 			set(unmodifiable.apply(newValues));
 
@@ -111,7 +113,7 @@ public final boolean removeAll(Collection<T> values) {
 		requireNonNull(values);
 		synchronized (lock) {
 			C newValues = create.get();
-			newValues.addAll(get());
+			newValues.addAll(getOrThrow());
 			boolean removed = newValues.removeAll(values);
 			set(unmodifiable.apply(newValues));
 
@@ -122,7 +124,7 @@ public final boolean removeAll(Collection<T> values) {
 	@Override
 	public final boolean contains(T value) {
 		synchronized (lock) {
-			return get().contains(value);
+			return getOrThrow().contains(value);
 		}
 	}
 
@@ -130,14 +132,14 @@ public final boolean contains(T value) {
 	public final boolean containsAll(Collection<T> values) {
 		requireNonNull(values);
 		synchronized (lock) {
-			return get().containsAll(values);
+			return getOrThrow().containsAll(values);
 		}
 	}
 
 	@Override
 	public final boolean empty() {
 		synchronized (lock) {
-			return get().isEmpty();
+			return getOrThrow().isEmpty();
 		}
 	}
 
@@ -149,7 +151,7 @@ public final boolean notEmpty() {
 	@Override
 	public final int size() {
 		synchronized (lock) {
-			return get().size();
+			return getOrThrow().size();
 		}
 	}
 
@@ -187,14 +189,14 @@ private SingleValue() {
 		}
 
 		@Override
-		protected synchronized T getValue() {
-			C collection = DefaultValues.this.get();
+		protected synchronized @Nullable T getValue() {
+			C collection = DefaultValues.this.getOrThrow();
 
 			return collection.isEmpty() ? null : collection.iterator().next();
 		}
 
 		@Override
-		protected synchronized void setValue(T value) {
+		protected synchronized void setValue(@Nullable T value) {
 			DefaultValues.this.set(value == null ? emptyList() : singleton(value));
 		}
 	}
diff --git a/common/core/src/main/java/is/codion/common/value/Value.java b/common/core/src/main/java/is/codion/common/value/Value.java
index 95f0a2e47f..7324febd81 100755
--- a/common/core/src/main/java/is/codion/common/value/Value.java
+++ b/common/core/src/main/java/is/codion/common/value/Value.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -80,7 +82,7 @@ enum Notify {
 	 * @see #addValidator(Validator)
 	 */
 	@Override
-	default void accept(T value) {
+	default void accept(@Nullable T value) {
 		set(value);
 	}
 
@@ -91,7 +93,7 @@ default void accept(T value) {
 	 * @throws IllegalArgumentException in case the given value is invalid
 	 * @see #addValidator(Validator)
 	 */
-	boolean set(T value);
+	boolean set(@Nullable T value);
 
 	/**
 	 * Clears this value, by setting it to null or the null value in case this is a non-null value.
@@ -192,7 +194,7 @@ static <T> Value<T> value() {
 	 * @param value the initial value
 	 * @return a Value for the given type
 	 */
-	static <T> Value<T> value(T value) {
+	static <T> Value<T> value(@Nullable T value) {
 		return builder()
 						.nullable(value)
 						.build();
@@ -228,7 +230,7 @@ interface BuilderFactory {
 		 * @param <T> the value type
 		 * @return a builder for a nullable {@link Value}
 		 */
-		<T> Builder<T, ?> nullable(T value);
+		<T> Builder<T, ?> nullable(@Nullable T value);
 	}
 
 	/**
@@ -242,7 +244,7 @@ interface Builder<T, B extends Builder<T, B>> {
 		 * @param value the initial value
 		 * @return this builder instance
 		 */
-		B value(T value);
+		B value(@Nullable T value);
 
 		/**
 		 * @param notify the notify policy for this value, default {@link Notify#WHEN_CHANGED}
@@ -314,6 +316,6 @@ interface Validator<T> {
 		 * @param value the value to validate
 		 * @throws IllegalArgumentException in case of an invalid value
 		 */
-		void validate(T value);
+		void validate(@Nullable T value);
 	}
 }
diff --git a/common/core/src/main/java/is/codion/common/value/ValueLink.java b/common/core/src/main/java/is/codion/common/value/ValueLink.java
index 84f01bbddf..8e676e647a 100644
--- a/common/core/src/main/java/is/codion/common/value/ValueLink.java
+++ b/common/core/src/main/java/is/codion/common/value/ValueLink.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Set;
 import java.util.function.Consumer;
 
@@ -107,14 +109,14 @@ private static final class LinkedValidator<T> implements Value.Validator<T> {
 
 		private final Value<T> linkedValue;
 
-		private Value.Validator<T> excluded;
+		private Value.@Nullable Validator<T> excluded;
 
 		private LinkedValidator(Value<T> linkedValue) {
 			this.linkedValue = linkedValue;
 		}
 
 		@Override
-		public void validate(T value) {
+		public void validate(@Nullable T value) {
 			if (linkedValue instanceof AbstractValue) {
 				((AbstractValue<T>) linkedValue).validators()
 								.stream()
diff --git a/common/core/src/main/java/is/codion/common/value/ValueObserver.java b/common/core/src/main/java/is/codion/common/value/ValueObserver.java
index b38f759bb1..2e752274d1 100644
--- a/common/core/src/main/java/is/codion/common/value/ValueObserver.java
+++ b/common/core/src/main/java/is/codion/common/value/ValueObserver.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.observer.Observer;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.NoSuchElementException;
 import java.util.Objects;
 import java.util.Optional;
@@ -35,7 +37,7 @@ public interface ValueObserver<T> extends Observer<T> {
 	/**
 	 * @return the value
 	 */
-	T get();
+	@Nullable T get();
 
 	/**
 	 * @return the value
@@ -96,7 +98,7 @@ default boolean isNotNull() {
 	 * @param value the value
 	 * @return true if the underlying value is equal to the given one
 	 */
-	default boolean isEqualTo(T value) {
+	default boolean isEqualTo(@Nullable T value) {
 		return Objects.equals(get(), value);
 	}
 
@@ -105,7 +107,7 @@ default boolean isEqualTo(T value) {
 	 * @param value the value
 	 * @return true if the underlying value is NOT equal to the given one
 	 */
-	default boolean isNotEqualTo(T value) {
+	default boolean isNotEqualTo(@Nullable T value) {
 		return !isEqualTo(value);
 	}
 }
diff --git a/common/core/src/main/java/is/codion/common/value/Values.java b/common/core/src/main/java/is/codion/common/value/Values.java
index 01adadcd72..ecee5601d5 100644
--- a/common/core/src/main/java/is/codion/common/value/Values.java
+++ b/common/core/src/main/java/is/codion/common/value/Values.java
@@ -18,6 +18,9 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+
 import java.util.Collection;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -31,12 +34,15 @@
  */
 public interface Values<T, C extends Collection<T>> extends Value<C>, ValuesObserver<T, C> {
 
+	@Override
+	@NonNull C get();
+
 	/**
 	 * Sets the values.
 	 * @param values the values to set
 	 * @return true if this {@link Values} instance changed
 	 */
-	boolean set(Collection<T> values);
+	boolean set(@Nullable Collection<T> values);
 
 	/**
 	 * Adds a value to this Values instance.
@@ -44,7 +50,7 @@ public interface Values<T, C extends Collection<T>> extends Value<C>, ValuesObse
 	 * @return true if the value was added
 	 * @see Collection#add(Object)
 	 */
-	boolean add(T value);
+	boolean add(@Nullable T value);
 
 	/**
 	 * Adds the given values to this Values instance.
@@ -68,7 +74,7 @@ public interface Values<T, C extends Collection<T>> extends Value<C>, ValuesObse
 	 * @return true if the value was removed
 	 * @see Collection#remove(Object)
 	 */
-	boolean remove(T value);
+	boolean remove(@Nullable T value);
 
 	/**
 	 * Removes the given values from this Values instance.
diff --git a/common/core/src/main/java/is/codion/common/value/ValuesObserver.java b/common/core/src/main/java/is/codion/common/value/ValuesObserver.java
index 7e5ea70113..273204229e 100644
--- a/common/core/src/main/java/is/codion/common/value/ValuesObserver.java
+++ b/common/core/src/main/java/is/codion/common/value/ValuesObserver.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.value;
 
+import org.jspecify.annotations.NonNull;
+
 import java.util.Collection;
 
 /**
@@ -27,6 +29,9 @@
  */
 public interface ValuesObserver<T, C extends Collection<T>> extends ValueObserver<C>, Iterable<T> {
 
+	@Override
+	@NonNull C get();
+
 	/**
 	 * Returns true if this {@link Values} instance contains the specified element
 	 * @param value the element
diff --git a/common/core/src/main/java/is/codion/common/value/package-info.java b/common/core/src/main/java/is/codion/common/value/package-info.java
new file mode 100644
index 0000000000..656b6659b8
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/value/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>{@link is.codion.common.value.Value} and related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.value;
\ No newline at end of file
diff --git a/common/core/src/main/java/is/codion/common/version/DefaultVersion.java b/common/core/src/main/java/is/codion/common/version/DefaultVersion.java
index ff8a3a91fc..2c3b5eb68d 100644
--- a/common/core/src/main/java/is/codion/common/version/DefaultVersion.java
+++ b/common/core/src/main/java/is/codion/common/version/DefaultVersion.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.version;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 import java.util.Objects;
@@ -33,8 +35,8 @@ final class DefaultVersion implements Version, Serializable {
 	private final int major;
 	private final int minor;
 	private final int patch;
-	private final String metadata;
-	private final String build;
+	private final @Nullable String metadata;
+	private final @Nullable String build;
 
 	private DefaultVersion(DefaulBuilder builder) {
 		this.major = builder.major;
@@ -109,7 +111,7 @@ public int compareTo(Version version) {
 		return result;
 	}
 
-	private static int compareMetadata(String metadata, String toCompare) {
+	private static int compareMetadata(@Nullable String metadata, @Nullable String toCompare) {
 		if (metadata != null && toCompare != null) {
 			return metadata.compareToIgnoreCase(toCompare);
 		}
@@ -128,8 +130,8 @@ static final class DefaulBuilder implements Builder {
 		private int major = 0;
 		private int minor = 0;
 		private int patch = 0;
-		private String metadata;
-		private String build;
+		private @Nullable String metadata;
+		private @Nullable String build;
 
 		@Override
 		public Builder major(int major) {
@@ -159,13 +161,13 @@ public Builder patch(int patch) {
 		}
 
 		@Override
-		public Builder metadata(String metadata) {
+		public Builder metadata(@Nullable String metadata) {
 			this.metadata = metadata;
 			return this;
 		}
 
 		@Override
-		public Builder build(String build) {
+		public Builder build(@Nullable String build) {
 			this.build = build;
 			return this;
 		}
diff --git a/common/core/src/main/java/is/codion/common/version/Version.java b/common/core/src/main/java/is/codion/common/version/Version.java
index ff3b29ddbd..d10f9cb346 100644
--- a/common/core/src/main/java/is/codion/common/version/Version.java
+++ b/common/core/src/main/java/is/codion/common/version/Version.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.version;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Optional;
@@ -88,13 +90,13 @@ interface Builder {
 		 * @param metadata the metadata version component
 		 * @return this builder instance
 		 */
-		Builder metadata(String metadata);
+		Builder metadata(@Nullable String metadata);
 
 		/**
 		 * @param build the build information version component
 		 * @return this builder instance
 		 */
-		Builder build(String build);
+		Builder build(@Nullable String build);
 
 		/**
 		 * @return a new {@link Version} instance based on this builder
diff --git a/common/core/src/main/java/is/codion/common/version/package-info.java b/common/core/src/main/java/is/codion/common/version/package-info.java
new file mode 100644
index 0000000000..890fda8dc8
--- /dev/null
+++ b/common/core/src/main/java/is/codion/common/version/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>See {@link is.codion.common.version.Version}.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.version;
\ No newline at end of file
diff --git a/common/core/src/main/java/module-info.java b/common/core/src/main/java/module-info.java
index 9b686efbaf..5462bbfe76 100644
--- a/common/core/src/main/java/module-info.java
+++ b/common/core/src/main/java/module-info.java
@@ -17,7 +17,7 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Common classes used throughout, such as:
+ * <p>Common classes used throughout.
  * <ul>
  * <li>{@link is.codion.common.observer.Observer}
  * <li>{@link is.codion.common.observer.Observable}
@@ -36,7 +36,9 @@
  * @uses is.codion.common.logging.LoggerProxy
  * @uses is.codion.common.resource.Resources
  */
+@org.jspecify.annotations.NullMarked
 module is.codion.common.core {
+	requires transitive org.jspecify;
 	exports is.codion.common;
 	exports is.codion.common.event;
 	exports is.codion.common.format;
diff --git a/common/core/src/test/java/is/codion/common/NullsTest.java b/common/core/src/test/java/is/codion/common/NullsTest.java
index d76d76d660..836879cec7 100644
--- a/common/core/src/test/java/is/codion/common/NullsTest.java
+++ b/common/core/src/test/java/is/codion/common/NullsTest.java
@@ -30,7 +30,7 @@ void nonNull() {
 		assertTrue(Nulls.nonNull());
 		assertTrue(Nulls.nonNull(new Object[0]));
 		assertTrue(Nulls.nonNull(1));
-		assertFalse(Nulls.nonNull(null));
+		assertFalse(Nulls.nonNull((Object[]) null));
 		assertFalse(Nulls.nonNull(1, null));
 		assertFalse(Nulls.nonNull(null, 1));
 	}
diff --git a/common/db/src/main/java/is/codion/common/db/connection/DatabaseConnection.java b/common/db/src/main/java/is/codion/common/db/connection/DatabaseConnection.java
index b3eb22d0a5..b7e0c5846a 100644
--- a/common/db/src/main/java/is/codion/common/db/connection/DatabaseConnection.java
+++ b/common/db/src/main/java/is/codion/common/db/connection/DatabaseConnection.java
@@ -23,6 +23,8 @@
 import is.codion.common.logging.MethodLogger;
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.Connection;
 import java.sql.SQLException;
 
@@ -67,7 +69,7 @@ public interface DatabaseConnection extends AutoCloseable {
 	 * until a non-null connection is set.
 	 * @param connection the JDBC connection
 	 */
-	void setConnection(Connection connection);
+	void setConnection(@Nullable Connection connection);
 
 	/**
 	 * Starts a transaction on this connection, to end the transaction use {@link #commitTransaction()} or {@link #rollbackTransaction()}.
@@ -130,12 +132,12 @@ public interface DatabaseConnection extends AutoCloseable {
 	/**
 	 * @param methodLogger the MethodLogger to use, null to disable method logging
 	 */
-	void setMethodLogger(MethodLogger methodLogger);
+	void setMethodLogger(@Nullable MethodLogger methodLogger);
 
 	/**
 	 * @return the MethodLogger being used, possibly null
 	 */
-	MethodLogger getMethodLogger();
+	@Nullable MethodLogger getMethodLogger();
 
 	/**
 	 * Constructs a new DatabaseConnection instance, based on the given Database and User
diff --git a/common/db/src/main/java/is/codion/common/db/connection/DefaultDatabaseConnection.java b/common/db/src/main/java/is/codion/common/db/connection/DefaultDatabaseConnection.java
index 302d11420c..0288cb3508 100644
--- a/common/db/src/main/java/is/codion/common/db/connection/DefaultDatabaseConnection.java
+++ b/common/db/src/main/java/is/codion/common/db/connection/DefaultDatabaseConnection.java
@@ -23,6 +23,8 @@
 import is.codion.common.logging.MethodLogger;
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.Connection;
 import java.sql.SQLException;
 import java.util.Map;
@@ -41,10 +43,10 @@ final class DefaultDatabaseConnection implements DatabaseConnection {
 	private final User user;
 	private final Database database;
 
-	private Connection connection;
+	private @Nullable Connection connection;
 	private boolean transactionOpen = false;
 
-	private MethodLogger methodLogger;
+	private @Nullable MethodLogger methodLogger;
 
 	/**
 	 * Constructs a new DefaultDatabaseConnection instance, initialized and ready for use.
@@ -83,12 +85,12 @@ public User user() {
 	}
 
 	@Override
-	public void setMethodLogger(MethodLogger methodLogger) {
+	public void setMethodLogger(@Nullable MethodLogger methodLogger) {
 		this.methodLogger = methodLogger;
 	}
 
 	@Override
-	public MethodLogger getMethodLogger() {
+	public @Nullable MethodLogger getMethodLogger() {
 		return methodLogger;
 	}
 
@@ -123,15 +125,13 @@ public boolean valid() {
 	}
 
 	@Override
-	public void setConnection(Connection connection) {
+	public void setConnection(@Nullable Connection connection) {
 		this.connection = connection;
 	}
 
 	@Override
 	public Connection getConnection() {
-		verifyOpenConnection();
-
-		return connection;
+		return verifyOpenConnection();
 	}
 
 	@Override
@@ -144,7 +144,7 @@ public void startTransaction() {
 		if (transactionOpen) {
 			throw new IllegalStateException("Transaction already open");
 		}
-		verifyOpenConnection();
+		connection = verifyOpenConnection();
 		logEntry("startTransaction");
 		transactionOpen = true;
 		logExit("startTransaction", null);
@@ -155,7 +155,7 @@ public void rollbackTransaction() throws SQLException {
 		if (!transactionOpen) {
 			throw new IllegalStateException("Transaction is not open");
 		}
-		verifyOpenConnection();
+		connection = verifyOpenConnection();
 		logEntry("rollbackTransaction");
 		SQLException exception = null;
 		try {
@@ -176,7 +176,7 @@ public void commitTransaction() throws SQLException {
 		if (!transactionOpen) {
 			throw new IllegalStateException("Transaction is not open");
 		}
-		verifyOpenConnection();
+		connection = verifyOpenConnection();
 		logEntry("commitTransaction");
 		SQLException exception = null;
 		try {
@@ -202,7 +202,7 @@ public void commit() throws SQLException {
 		if (transactionOpen) {
 			throw new IllegalStateException("Can not perform a commit during an open transaction, use 'commitTransaction()'");
 		}
-		verifyOpenConnection();
+		connection = verifyOpenConnection();
 		logEntry("commit");
 		SQLException exception = null;
 		try {
@@ -223,7 +223,7 @@ public void rollback() throws SQLException {
 		if (transactionOpen) {
 			throw new IllegalStateException("Can not perform a rollback during an open transaction, use 'rollbackTransaction()'");
 		}
-		verifyOpenConnection();
+		connection = verifyOpenConnection();
 		logEntry("rollback");
 		SQLException exception = null;
 		try {
@@ -244,7 +244,7 @@ private void logEntry(String method) {
 		}
 	}
 
-	private MethodLogger.Entry logExit(String method, Exception exception) {
+	private MethodLogger.@Nullable Entry logExit(String method, @Nullable Exception exception) {
 		if (methodLogger != null && methodLogger.isEnabled()) {
 			return methodLogger.exit(method, exception);
 		}
@@ -252,10 +252,12 @@ private MethodLogger.Entry logExit(String method, Exception exception) {
 		return null;
 	}
 
-	private void verifyOpenConnection() {
+	private Connection verifyOpenConnection() {
 		if (!connected()) {
 			throw new IllegalStateException("Connection is closed");
 		}
+
+		return connection;
 	}
 
 	/**
diff --git a/common/db/src/main/java/is/codion/common/db/connection/package-info.java b/common/db/src/main/java/is/codion/common/db/connection/package-info.java
new file mode 100644
index 0000000000..9772fac181
--- /dev/null
+++ b/common/db/src/main/java/is/codion/common/db/connection/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>JDBC connection related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.db.connection;
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/database/AbstractDatabase.java b/common/db/src/main/java/is/codion/common/db/database/AbstractDatabase.java
index dd755ca20f..e0c97183bf 100644
--- a/common/db/src/main/java/is/codion/common/db/database/AbstractDatabase.java
+++ b/common/db/src/main/java/is/codion/common/db/database/AbstractDatabase.java
@@ -27,6 +27,8 @@
 import is.codion.common.db.pool.ConnectionPoolWrapper;
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 import java.sql.Connection;
@@ -66,11 +68,11 @@ public abstract class AbstractDatabase implements Database {
 		DriverManager.setLoginTimeout(Database.LOGIN_TIMEOUT.getOrThrow());
 	}
 
-	private static Database instance;
+	private static @Nullable Database instance;
 
 	private final Map<String, ConnectionPoolWrapper> connectionPools = new HashMap<>();
-	private final int validityCheckTimeout = CONNECTION_VALIDITY_CHECK_TIMEOUT.get();
-	private final Integer transactionIsolation = TRANSACTION_ISOLATION.get();
+	private final int validityCheckTimeout = CONNECTION_VALIDITY_CHECK_TIMEOUT.getOrThrow();
+	private final	@Nullable Integer transactionIsolation = TRANSACTION_ISOLATION.get();
 	private final DefaultQueryCounter queryCounter = new DefaultQueryCounter();
 	private final String url;
 
@@ -198,7 +200,7 @@ public String sequenceQuery(String sequenceName) {
 	}
 
 	@Override
-	public String errorMessage(SQLException exception, Operation operation) {
+	public @Nullable String errorMessage(SQLException exception, Operation operation) {
 		requireNonNull(exception);
 		requireNonNull(operation);
 
@@ -249,7 +251,7 @@ else if (isTimeoutException(exception)) {
 	static Database instance() {
 		try {
 			synchronized (AbstractDatabase.class) {
-				String databaseUrl = DATABASE_URL.get();
+				String databaseUrl = DATABASE_URL.getOrThrow();
 				if (AbstractDatabase.instance == null || !AbstractDatabase.instance.url().equals(databaseUrl)) {
 					Database previousInstance = AbstractDatabase.instance;
 					//replace the instance
@@ -279,7 +281,7 @@ static Database instance() {
 	 * @param offset the offset, may be null
 	 * @return a limit/offset clause
 	 */
-	protected static String createLimitOffsetClause(Integer limit, Integer offset) {
+	protected static String createLimitOffsetClause(@Nullable Integer limit, @Nullable Integer offset) {
 		StringBuilder builder = new StringBuilder();
 		if (limit != null) {
 			builder.append(LIMIT).append(limit);
@@ -299,7 +301,7 @@ protected static String createLimitOffsetClause(Integer limit, Integer offset) {
 	 * @param offset the offset, may be null
 	 * @return a limit/offset clause
 	 */
-	protected static String createOffsetFetchNextClause(Integer limit, Integer offset) {
+	protected static String createOffsetFetchNextClause(@Nullable Integer limit, @Nullable Integer offset) {
 		StringBuilder builder = new StringBuilder();
 		if (offset != null) {
 			builder.append(OFFSET).append(offset).append(ROWS);
@@ -347,7 +349,7 @@ private static final class DefaultQueryCounter implements QueryCounter {
 		private final AtomicInteger deletesPerSecondCounter = new AtomicInteger();
 		private final AtomicInteger otherPerSecondCounter = new AtomicInteger();
 
-		private final boolean enabled = COUNT_QUERIES.get();
+		private final boolean enabled = COUNT_QUERIES.getOrThrow();
 
 		@Override
 		public void select() {
diff --git a/common/db/src/main/java/is/codion/common/db/database/Database.java b/common/db/src/main/java/is/codion/common/db/database/Database.java
index 78b3b73ebe..25f744b153 100644
--- a/common/db/src/main/java/is/codion/common/db/database/Database.java
+++ b/common/db/src/main/java/is/codion/common/db/database/Database.java
@@ -26,6 +26,8 @@
 import is.codion.common.property.PropertyValue;
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.SQLException;
 import java.util.Collection;
 
@@ -161,12 +163,12 @@ enum Operation {
 
 	/**
 	 * Returns a limit/offset clause variation for this database, based on the given limit and offset values.
-	 * If both are null an empty string should be returned.
+	 * If both are null an empty string is returned.
 	 * @param limit the limit
 	 * @param offset the offset
 	 * @return a limit/offset clause
 	 */
-	String limitOffsetClause(Integer limit, Integer offset);
+	String limitOffsetClause(@Nullable Integer limit, @Nullable Integer offset);
 
 	/**
 	 * Returns true if this database requires that subqueries by aliased.
@@ -189,7 +191,7 @@ enum Operation {
 	 * @return the message assigned to the given exception
 	 * @throws NullPointerException in case {@code exception} or {@code operation} is null
 	 */
-	String errorMessage(SQLException exception, Operation operation);
+	@Nullable String errorMessage(SQLException exception, Operation operation);
 
 	/**
 	 * Maps the given SQLException to a DatabaseException.
@@ -262,7 +264,7 @@ enum Operation {
 
 	/**
 	 * @param username the username
-	 * @return the connection pool for the given user, null if none exists
+	 * @return the connection pool for the given user
 	 * @throws IllegalArgumentException in case no connection pool exists for the given user
 	 */
 	ConnectionPoolWrapper connectionPool(String username);
diff --git a/common/db/src/main/java/is/codion/common/db/database/package-info.java b/common/db/src/main/java/is/codion/common/db/database/package-info.java
index 0a768ca31e..5a1ec6b005 100644
--- a/common/db/src/main/java/is/codion/common/db/database/package-info.java
+++ b/common/db/src/main/java/is/codion/common/db/database/package-info.java
@@ -17,7 +17,8 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>Database related classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.db.database.Database#DATABASE_URL}
  * <li>{@link is.codion.common.db.database.Database#DATABASE_INIT_SCRIPTS}
@@ -28,4 +29,5 @@
  * <li>{@link is.codion.common.db.database.Database#CONNECTION_VALIDITY_CHECK_TIMEOUT}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common.db.database;
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/exception/AuthenticationException.java b/common/db/src/main/java/is/codion/common/db/exception/AuthenticationException.java
index 19d0a421c2..991d23f67c 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/AuthenticationException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/AuthenticationException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * An exception indication an authentication failure
  */
@@ -26,7 +28,7 @@ public final class AuthenticationException extends DatabaseException {
 	/**
 	 * @param message the error message
 	 */
-	public AuthenticationException(String message) {
+	public AuthenticationException(@Nullable String message) {
 		super(message);
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/DatabaseException.java b/common/db/src/main/java/is/codion/common/db/exception/DatabaseException.java
index ffeed5df76..49cc702ec8 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/DatabaseException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/DatabaseException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.sql.SQLException;
 import java.util.Optional;
@@ -34,7 +36,7 @@ public class DatabaseException extends RuntimeException {
 	 * The sql statement being run when this exception occurred, if any, transient
 	 * so that it's not available client side if running in a server/client environment
 	 */
-	private final transient String statement;
+	private final transient @Nullable String statement;
 
 	/**
 	 * The underlying error code, if any, transient so that it's not
@@ -46,13 +48,13 @@ public class DatabaseException extends RuntimeException {
 	 * The underlying sql state, if any, transient so that it's not
 	 * available client side if running in a server/client environment
 	 */
-	private final transient String sqlState;
+	private final transient @Nullable String sqlState;
 
 	/**
 	 * Constructs a new DatabaseException instance
 	 * @param message the exception message
 	 */
-	public DatabaseException(String message) {
+	public DatabaseException(@Nullable String message) {
 		this(message, null);
 	}
 
@@ -61,7 +63,7 @@ public DatabaseException(String message) {
 	 * @param message the exception message
 	 * @param statement the sql statement which caused the exception
 	 */
-	public DatabaseException(String message, String statement) {
+	public DatabaseException(@Nullable String message, @Nullable String statement) {
 		super(message);
 		this.statement = statement;
 		this.errorCode = -1;
@@ -81,7 +83,7 @@ public DatabaseException(SQLException cause) {
 	 * @param cause the root cause, the stack trace is copied and used
 	 * @param message the exception message
 	 */
-	public DatabaseException(SQLException cause, String message) {
+	public DatabaseException(SQLException cause, @Nullable String message) {
 		this(cause, message, null);
 	}
 
@@ -91,7 +93,7 @@ public DatabaseException(SQLException cause, String message) {
 	 * @param message the exception message
 	 * @param statement the sql statement which caused the exception
 	 */
-	public DatabaseException(SQLException cause, String message, String statement) {
+	public DatabaseException(@Nullable SQLException cause, @Nullable String message, @Nullable String statement) {
 		super(message);
 		this.statement = statement;
 		if (cause != null) {
diff --git a/common/db/src/main/java/is/codion/common/db/exception/DeleteException.java b/common/db/src/main/java/is/codion/common/db/exception/DeleteException.java
index c04660d697..d2fe836a14 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/DeleteException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/DeleteException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * An exception indicating a failed delete operation
  */
@@ -27,7 +29,7 @@ public final class DeleteException extends DatabaseException {
 	 * Instantiates a new {@link DeleteException}
 	 * @param message the message
 	 */
-	public DeleteException(String message) {
+	public DeleteException(@Nullable String message) {
 		super(message);
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/MultipleRecordsFoundException.java b/common/db/src/main/java/is/codion/common/db/exception/MultipleRecordsFoundException.java
index 32e287d655..710c81978d 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/MultipleRecordsFoundException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/MultipleRecordsFoundException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Exception used when one record was expected but many were found.
  */
@@ -27,7 +29,7 @@ public class MultipleRecordsFoundException extends DatabaseException {
 	 * Instantiates a new MultipleRecordsFoundException
 	 * @param message the exception message
 	 */
-	public MultipleRecordsFoundException(String message) {
+	public MultipleRecordsFoundException(@Nullable String message) {
 		super(message);
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/QueryTimeoutException.java b/common/db/src/main/java/is/codion/common/db/exception/QueryTimeoutException.java
index f9ba208839..cc40f82499 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/QueryTimeoutException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/QueryTimeoutException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.SQLException;
 
 /**
@@ -30,7 +32,7 @@ public final class QueryTimeoutException extends DatabaseException {
 	 * @param cause the underlying cause
 	 * @param message the error message
 	 */
-	public QueryTimeoutException(SQLException cause, String message) {
+	public QueryTimeoutException(SQLException cause, @Nullable String message) {
 		super(cause, message);
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/RecordModifiedException.java b/common/db/src/main/java/is/codion/common/db/exception/RecordModifiedException.java
index e0b0566648..a5c7ff1550 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/RecordModifiedException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/RecordModifiedException.java
@@ -18,13 +18,17 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
+import static java.util.Objects.requireNonNull;
+
 /**
  * An exception indicating that the row in question has been modified or deleted since it was loaded.
  */
 public final class RecordModifiedException extends UpdateException {
 
 	private final Object row;
-	private final Object modifiedRow;
+	private final @Nullable Object modifiedRow;
 
 	/**
 	 * Instantiates a new RecordModifiedException
@@ -32,9 +36,9 @@ public final class RecordModifiedException extends UpdateException {
 	 * @param modifiedRow the current (modified) version of the row, null if it has been deleted
 	 * @param message a message describing the modification
 	 */
-	public RecordModifiedException(Object row, Object modifiedRow, String message) {
+	public RecordModifiedException(Object row, @Nullable Object modifiedRow, @Nullable String message) {
 		super(message);
-		this.row = row;
+		this.row = requireNonNull(row);
 		this.modifiedRow = modifiedRow;
 	}
 
@@ -48,7 +52,7 @@ public Object row() {
 	/**
 	 * @return the current (modified) version of the row, null if it has been deleted
 	 */
-	public Object modifiedRow() {
+	public @Nullable Object modifiedRow() {
 		return modifiedRow;
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/ReferentialIntegrityException.java b/common/db/src/main/java/is/codion/common/db/exception/ReferentialIntegrityException.java
index 2874cafa11..8cdb9e32ec 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/ReferentialIntegrityException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/ReferentialIntegrityException.java
@@ -20,6 +20,8 @@
 
 import is.codion.common.db.database.Database.Operation;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.SQLException;
 
 import static java.util.Objects.requireNonNull;
@@ -37,7 +39,7 @@ public final class ReferentialIntegrityException extends DatabaseException {
 	 * @param message the error message
 	 * @param operation the operation causing this exception
 	 */
-	public ReferentialIntegrityException(SQLException cause, String message, Operation operation) {
+	public ReferentialIntegrityException(SQLException cause, @Nullable String message, Operation operation) {
 		super(cause, message);
 		this.operation = requireNonNull(operation);
 	}
diff --git a/common/db/src/main/java/is/codion/common/db/exception/UniqueConstraintException.java b/common/db/src/main/java/is/codion/common/db/exception/UniqueConstraintException.java
index 8a1cec177d..6b23141c44 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/UniqueConstraintException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/UniqueConstraintException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.SQLException;
 
 /**
@@ -30,7 +32,7 @@ public final class UniqueConstraintException extends DatabaseException {
 	 * @param cause the underlying cause
 	 * @param message the error message
 	 */
-	public UniqueConstraintException(SQLException cause, String message) {
+	public UniqueConstraintException(SQLException cause, @Nullable String message) {
 		super(cause, message);
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/UpdateException.java b/common/db/src/main/java/is/codion/common/db/exception/UpdateException.java
index 5461d78759..5c6e22b14c 100644
--- a/common/db/src/main/java/is/codion/common/db/exception/UpdateException.java
+++ b/common/db/src/main/java/is/codion/common/db/exception/UpdateException.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.exception;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * An exception indicating a failed update operation
  */
@@ -27,7 +29,7 @@ public class UpdateException extends DatabaseException {
 	 * Instantiates a new {@link UpdateException}
 	 * @param message the message
 	 */
-	public UpdateException(String message) {
+	public UpdateException(@Nullable String message) {
 		super(message);
 	}
 }
diff --git a/common/db/src/main/java/is/codion/common/db/exception/package-info.java b/common/db/src/main/java/is/codion/common/db/exception/package-info.java
new file mode 100644
index 0000000000..0795584d9f
--- /dev/null
+++ b/common/db/src/main/java/is/codion/common/db/exception/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Database related Exceptions.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.db.exception;
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/operation/DatabaseFunction.java b/common/db/src/main/java/is/codion/common/db/operation/DatabaseFunction.java
index 7bad0c4b9f..8299e0c519 100644
--- a/common/db/src/main/java/is/codion/common/db/operation/DatabaseFunction.java
+++ b/common/db/src/main/java/is/codion/common/db/operation/DatabaseFunction.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.operation;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * A database function
  * @param <C> the connection type required by this function
@@ -32,5 +34,5 @@ public interface DatabaseFunction<C, T, R> {
 	 * @param argument the function argument, if any
 	 * @return the function return argument
 	 */
-	R execute(C connection, T argument);
+	@Nullable R execute(C connection, @Nullable T argument);
 }
diff --git a/common/db/src/main/java/is/codion/common/db/operation/DatabaseProcedure.java b/common/db/src/main/java/is/codion/common/db/operation/DatabaseProcedure.java
index b46294ee6a..edec9fbf1c 100644
--- a/common/db/src/main/java/is/codion/common/db/operation/DatabaseProcedure.java
+++ b/common/db/src/main/java/is/codion/common/db/operation/DatabaseProcedure.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.operation;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * A database procedure
  * @param <C> the connection type required by this procedure
@@ -30,5 +32,5 @@ public interface DatabaseProcedure<C, T> {
 	 * @param connection the connection to use
 	 * @param argument the procedure argument, if any
 	 */
-	void execute(C connection, T argument);
+	void execute(C connection, @Nullable T argument);
 }
diff --git a/common/db/src/main/java/is/codion/common/db/operation/package-info.java b/common/db/src/main/java/is/codion/common/db/operation/package-info.java
new file mode 100644
index 0000000000..cbf8cb4e39
--- /dev/null
+++ b/common/db/src/main/java/is/codion/common/db/operation/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Database operations and functions.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.db.operation;
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/pool/AbstractConnectionPoolWrapper.java b/common/db/src/main/java/is/codion/common/db/pool/AbstractConnectionPoolWrapper.java
index b29777db85..7edd5a5272 100755
--- a/common/db/src/main/java/is/codion/common/db/pool/AbstractConnectionPoolWrapper.java
+++ b/common/db/src/main/java/is/codion/common/db/pool/AbstractConnectionPoolWrapper.java
@@ -25,6 +25,8 @@
 import is.codion.common.proxy.ProxyBuilder.ProxyMethod;
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
+
 import javax.sql.DataSource;
 import java.sql.Connection;
 import java.sql.SQLException;
@@ -198,7 +200,7 @@ public Object invoke(Parameters<DataSource> parameters) throws Throwable {
 	private final class Close implements ProxyMethod<Connection> {
 
 		@Override
-		public Object invoke(Parameters<Connection> parameters) throws Throwable {
+		public @Nullable Object invoke(Parameters<Connection> parameters) throws Throwable {
 			Connection connection = parameters.delegate();
 			if (!connection.isClosed()) {
 				counter.incrementConnectionsDestroyedCounter();
diff --git a/common/db/src/main/java/is/codion/common/db/pool/package-info.java b/common/db/src/main/java/is/codion/common/db/pool/package-info.java
index a6f4af25a1..feed9aaee6 100644
--- a/common/db/src/main/java/is/codion/common/db/pool/package-info.java
+++ b/common/db/src/main/java/is/codion/common/db/pool/package-info.java
@@ -17,11 +17,13 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>Connection pool related classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.db.pool.ConnectionPoolWrapper#DEFAULT_MAXIMUM_POOL_SIZE}
  * <li>{@link is.codion.common.db.pool.ConnectionPoolWrapper#DEFAULT_MINIMUM_POOL_SIZE}
  * <li>{@link is.codion.common.db.pool.ConnectionPoolWrapper#DEFAULT_IDLE_TIMEOUT}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common.db.pool;
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/report/AbstractReport.java b/common/db/src/main/java/is/codion/common/db/report/AbstractReport.java
index c8e9d1fd55..eb42e4b8a5 100644
--- a/common/db/src/main/java/is/codion/common/db/report/AbstractReport.java
+++ b/common/db/src/main/java/is/codion/common/db/report/AbstractReport.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.report;
 
+import org.jspecify.annotations.Nullable;
+
 import static java.util.Objects.requireNonNull;
 
 /**
@@ -35,7 +37,7 @@ public abstract class AbstractReport<T, R, P> implements Report<T, R, P> {
 
 	private final boolean cacheReport;
 
-	private T cachedReport;
+	private @Nullable T cachedReport;
 
 	/**
 	 * Instantiates a new AbstractReport.
diff --git a/common/db/src/main/java/is/codion/common/db/report/package-info.java b/common/db/src/main/java/is/codion/common/db/report/package-info.java
index 49fbe4efd5..205906a8b6 100644
--- a/common/db/src/main/java/is/codion/common/db/report/package-info.java
+++ b/common/db/src/main/java/is/codion/common/db/report/package-info.java
@@ -17,10 +17,12 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>Report related classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.db.report.Report#REPORT_PATH}
  * <li>{@link is.codion.common.db.report.Report#CACHE_REPORTS}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common.db.report;
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/result/DefaultIterator.java b/common/db/src/main/java/is/codion/common/db/result/DefaultIterator.java
index 35d57393fe..904f52d72f 100644
--- a/common/db/src/main/java/is/codion/common/db/result/DefaultIterator.java
+++ b/common/db/src/main/java/is/codion/common/db/result/DefaultIterator.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.result;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.SQLException;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
@@ -43,7 +45,7 @@ public boolean hasNext() {
 	}
 
 	@Override
-	public T next() {
+	public @Nullable T next() {
 		if (!hasNext()) {
 			throw new NoSuchElementException();
 		}
diff --git a/common/db/src/main/java/is/codion/common/db/result/ResultIterator.java b/common/db/src/main/java/is/codion/common/db/result/ResultIterator.java
index 8e1c785b01..0a9dda109c 100644
--- a/common/db/src/main/java/is/codion/common/db/result/ResultIterator.java
+++ b/common/db/src/main/java/is/codion/common/db/result/ResultIterator.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.result;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.SQLException;
 import java.util.Iterator;
 
@@ -40,7 +42,7 @@ public interface ResultIterator<T> extends AutoCloseable, Iterable<T> {
 	 * @throws SQLException in case of an exception
 	 * @throws java.util.NoSuchElementException in case no more rows are available
 	 */
-	T next() throws SQLException;
+	@Nullable T next() throws SQLException;
 
 	/**
 	 * Closes the underlying result set and other resources held by this iterator
diff --git a/common/db/src/main/java/is/codion/common/db/result/ResultPacker.java b/common/db/src/main/java/is/codion/common/db/result/ResultPacker.java
index 4c531f0965..da387ca7b6 100644
--- a/common/db/src/main/java/is/codion/common/db/result/ResultPacker.java
+++ b/common/db/src/main/java/is/codion/common/db/result/ResultPacker.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.db.result;
 
+import org.jspecify.annotations.Nullable;
+
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.ArrayList;
@@ -59,5 +61,5 @@ default List<T> pack(ResultSet resultSet) throws SQLException {
 	 * @return the instance fetched from the ResultSet
 	 * @throws SQLException in case of failure
 	 */
-	T get(ResultSet resultSet) throws SQLException;
+	@Nullable T get(ResultSet resultSet) throws SQLException;
 }
\ No newline at end of file
diff --git a/common/db/src/main/java/is/codion/common/db/result/package-info.java b/common/db/src/main/java/is/codion/common/db/result/package-info.java
new file mode 100644
index 0000000000..44d07024f8
--- /dev/null
+++ b/common/db/src/main/java/is/codion/common/db/result/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>ResultSet handling related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.db.result;
\ No newline at end of file
diff --git a/common/db/src/main/java/module-info.java b/common/db/src/main/java/module-info.java
index d731ebe78c..66f958eb51 100644
--- a/common/db/src/main/java/module-info.java
+++ b/common/db/src/main/java/module-info.java
@@ -17,7 +17,7 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Core classes concerned with JDBC connectivity, such as:
+ * <p>Core classes concerned with JDBC connectivity.
  * <ul>
  * <li>{@link is.codion.common.db.database.Database}
  * <li>{@link is.codion.common.db.database.DatabaseFactory}
@@ -29,7 +29,9 @@
  * @uses is.codion.common.db.database.DatabaseFactory
  * @uses is.codion.common.db.pool.ConnectionPoolFactory
  */
+@org.jspecify.annotations.NullMarked
 module is.codion.common.db {
+	requires transitive org.jspecify;
 	requires transitive java.sql;
 	requires transitive is.codion.common.core;
 
diff --git a/common/db/src/test/java/is/codion/common/db/database/AbstractDatabaseTest.java b/common/db/src/test/java/is/codion/common/db/database/AbstractDatabaseTest.java
index fa541e54c3..368cbc2438 100644
--- a/common/db/src/test/java/is/codion/common/db/database/AbstractDatabaseTest.java
+++ b/common/db/src/test/java/is/codion/common/db/database/AbstractDatabaseTest.java
@@ -109,7 +109,7 @@ public String name() {
 
 		@Override
 		public String autoIncrementQuery(String idSource) {
-			return null;
+			return "";
 		}
 
 		@Override
diff --git a/common/db/src/test/java/is/codion/common/db/database/DatabaseTest.java b/common/db/src/test/java/is/codion/common/db/database/DatabaseTest.java
index 75985c20a2..024843c373 100644
--- a/common/db/src/test/java/is/codion/common/db/database/DatabaseTest.java
+++ b/common/db/src/test/java/is/codion/common/db/database/DatabaseTest.java
@@ -20,6 +20,7 @@
 
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import java.sql.Connection;
@@ -59,7 +60,7 @@ public String selectForUpdateClause() {
 		}
 
 		@Override
-		public String limitOffsetClause(Integer limit, Integer offset) {
+		public String limitOffsetClause(@Nullable Integer limit, @Nullable Integer offset) {
 			return createLimitOffsetClause(limit, offset);
 		}
 
diff --git a/common/i18n/src/main/java/is/codion/common/i18n/package-info.java b/common/i18n/src/main/java/is/codion/common/i18n/package-info.java
new file mode 100644
index 0000000000..6bdc56761f
--- /dev/null
+++ b/common/i18n/src/main/java/is/codion/common/i18n/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>i18n related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.i18n;
\ No newline at end of file
diff --git a/common/i18n/src/main/java/module-info.java b/common/i18n/src/main/java/module-info.java
index 0bdda449ad..5dc6389413 100644
--- a/common/i18n/src/main/java/module-info.java
+++ b/common/i18n/src/main/java/module-info.java
@@ -22,7 +22,9 @@
  * <li>{@link is.codion.common.i18n.Messages}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 module is.codion.common.i18n {
+	requires transitive org.jspecify;
 	requires is.codion.common.core;
 
 	exports is.codion.common.i18n;
diff --git a/common/model/src/main/java/is/codion/common/model/FilterModel.java b/common/model/src/main/java/is/codion/common/model/FilterModel.java
index b46c14635d..006c3c9561 100644
--- a/common/model/src/main/java/is/codion/common/model/FilterModel.java
+++ b/common/model/src/main/java/is/codion/common/model/FilterModel.java
@@ -29,6 +29,8 @@
 import is.codion.common.state.StateObserver;
 import is.codion.common.value.Value;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.Collection;
 import java.util.List;
 import java.util.function.Consumer;
@@ -299,7 +301,7 @@ abstract class AbstractRefresher<T> implements Refresher<T> {
 		private final Event<Exception> refreshFailedEvent = Event.event();
 		private final State refreshingState = State.state();
 		private final Supplier<Collection<T>> supplier;
-		private final State async = State.state(ASYNC_REFRESH.get());
+		private final State async = State.state(ASYNC_REFRESH.getOrThrow());
 
 		/**
 		 * @param supplier supplies the items when refreshing
@@ -389,13 +391,13 @@ protected final void notifyFailure(Exception exception) {
 		 * Performes an async refresh
 		 * @param onRefresh if specified will be called after a successful refresh
 		 */
-		protected abstract void refreshAsync(Consumer<Collection<T>> onRefresh);
+		protected abstract void refreshAsync(@Nullable Consumer<Collection<T>> onRefresh);
 
 		/**
 		 * Performs a sync refresh
 		 * @param onRefresh if specified will be called after a successful refresh
 		 */
-		protected abstract void refreshSync(Consumer<Collection<T>> onRefresh);
+		protected abstract void refreshSync(@Nullable Consumer<Collection<T>> onRefresh);
 
 		/**
 		 * Processes the refresh result, by replacing the current model items by the result items.
diff --git a/common/model/src/main/java/is/codion/common/model/UserPreferences.java b/common/model/src/main/java/is/codion/common/model/UserPreferences.java
index 3c730b46bb..e441f40891 100644
--- a/common/model/src/main/java/is/codion/common/model/UserPreferences.java
+++ b/common/model/src/main/java/is/codion/common/model/UserPreferences.java
@@ -18,6 +18,8 @@
  */
 package is.codion.common.model;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.prefs.BackingStoreException;
 import java.util.prefs.Preferences;
 
@@ -28,7 +30,7 @@
  */
 public final class UserPreferences {
 
-	private static Preferences preferences;
+	private static @Nullable Preferences preferences;
 
 	private UserPreferences() {}
 
diff --git a/common/model/src/main/java/is/codion/common/model/condition/ConditionModel.java b/common/model/src/main/java/is/codion/common/model/condition/ConditionModel.java
index 85049a3f24..8ecb069b03 100644
--- a/common/model/src/main/java/is/codion/common/model/condition/ConditionModel.java
+++ b/common/model/src/main/java/is/codion/common/model/condition/ConditionModel.java
@@ -26,6 +26,8 @@
 import is.codion.common.value.Value;
 import is.codion.common.value.ValueSet;
 
+import org.jspecify.annotations.Nullable;
+
 import java.text.Format;
 import java.util.List;
 import java.util.Optional;
@@ -166,7 +168,7 @@ public String description() {
 	 * @param value the value
 	 * @return true if the given value is accepted by this models condition
 	 */
-	boolean accepts(Comparable<T> value);
+	boolean accepts(@Nullable Comparable<T> value);
 
 	/**
 	 * @return an observer notified each time the condition changes
@@ -235,13 +237,13 @@ interface Builder<T> {
 		 * @param format the format to use when presenting the values, numbers for example
 		 * @return this builder instance
 		 */
-		Builder<T> format(Format format);
+		Builder<T> format(@Nullable Format format);
 
 		/**
 		 * @param dateTimePattern the date/time format pattern to use in case of a date/time value
 		 * @return this builder instance
 		 */
-		Builder<T> dateTimePattern(String dateTimePattern);
+		Builder<T> dateTimePattern(@Nullable String dateTimePattern);
 
 		/**
 		 * @param wildcard the wildcards to use
diff --git a/common/model/src/main/java/is/codion/common/model/condition/DefaultConditionModel.java b/common/model/src/main/java/is/codion/common/model/condition/DefaultConditionModel.java
index 5587e761ee..3893f65320 100644
--- a/common/model/src/main/java/is/codion/common/model/condition/DefaultConditionModel.java
+++ b/common/model/src/main/java/is/codion/common/model/condition/DefaultConditionModel.java
@@ -29,6 +29,8 @@
 import is.codion.common.value.ValueObserver;
 import is.codion.common.value.ValueSet;
 
+import org.jspecify.annotations.Nullable;
+
 import java.text.Format;
 import java.util.List;
 import java.util.Optional;
@@ -62,8 +64,8 @@ final class DefaultConditionModel<T> implements ConditionModel<T> {
 					.build();
 
 	private final Class<T> valueClass;
-	private final Format format;
-	private final String dateTimePattern;
+	private final @Nullable Format format;
+	private final @Nullable String dateTimePattern;
 	private final List<Operator> operators;
 
 	private DefaultConditionModel(DefaultBuilder<T> builder) {
@@ -162,7 +164,7 @@ public void clear() {
 	}
 
 	@Override
-	public boolean accepts(Comparable<T> value) {
+	public boolean accepts(@Nullable Comparable<T> value) {
 		return valueAccepted(value);
 	}
 
@@ -171,11 +173,11 @@ public Observer<?> changed() {
 		return conditionChanged.observer();
 	}
 
-	private boolean valueAccepted(Comparable<T> comparable) {
+	private boolean valueAccepted(@Nullable Comparable<T> comparable) {
 		if (!caseSensitive.get()) {
 			comparable = stringOrCharacterToLowerCase(comparable);
 		}
-		switch (operator.get()) {
+		switch (operator.getOrThrow()) {
 			case EQUAL:
 				return isEqual(comparable);
 			case NOT_EQUAL:
@@ -205,7 +207,7 @@ private boolean valueAccepted(Comparable<T> comparable) {
 		}
 	}
 
-	private boolean isEqual(Comparable<T> comparable) {
+	private boolean isEqual(@Nullable Comparable<T> comparable) {
 		T equalOperand = operands.equal().get();
 		if (!caseSensitive.get()) {
 			equalOperand = stringOrCharacterToLowerCase(equalOperand);
@@ -223,7 +225,7 @@ private boolean isEqual(Comparable<T> comparable) {
 		return comparable.compareTo(equalOperand) == 0;
 	}
 
-	private boolean isNotEqual(Comparable<T> comparable) {
+	private boolean isNotEqual(@Nullable Comparable<T> comparable) {
 		T equalOperand = operands.equal().get();
 		if (!caseSensitive.get()) {
 			equalOperand = stringOrCharacterToLowerCase(equalOperand);
@@ -261,31 +263,31 @@ private boolean isEqualWildcard(String value) {
 						.collect(joining(REGEX_WILDCARD, "", equalOperand.endsWith(WILDCARD_CHARACTER) ? REGEX_WILDCARD : "")), value);
 	}
 
-	private boolean isLessThan(Comparable<T> comparable) {
+	private boolean isLessThan(@Nullable Comparable<T> comparable) {
 		T upperBound = operands.upperBound.get();
 
 		return upperBound == null || comparable != null && comparable.compareTo(upperBound) < 0;
 	}
 
-	private boolean isLessThanOrEqual(Comparable<T> comparable) {
+	private boolean isLessThanOrEqual(@Nullable Comparable<T> comparable) {
 		T upperBound = operands.upperBound.get();
 
 		return upperBound == null || comparable != null && comparable.compareTo(upperBound) <= 0;
 	}
 
-	private boolean isGreaterThan(Comparable<T> comparable) {
+	private boolean isGreaterThan(@Nullable Comparable<T> comparable) {
 		T lowerBound = operands.lowerBound.get();
 
 		return lowerBound == null || comparable != null && comparable.compareTo(lowerBound) > 0;
 	}
 
-	private boolean isGreaterThanOrEqual(Comparable<T> comparable) {
+	private boolean isGreaterThanOrEqual(@Nullable Comparable<T> comparable) {
 		T lowerBound = operands.lowerBound.get();
 
 		return lowerBound == null || comparable != null && comparable.compareTo(lowerBound) >= 0;
 	}
 
-	private boolean isBetweenExclusive(Comparable<T> comparable) {
+	private boolean isBetweenExclusive(@Nullable Comparable<T> comparable) {
 		T lowerBound = operands.lowerBound.get();
 		T upperBound = operands.upperBound.get();
 		if (lowerBound == null && upperBound == null) {
@@ -310,7 +312,7 @@ private boolean isBetweenExclusive(Comparable<T> comparable) {
 		return lowerCompareResult > 0 && upperCompareResult < 0;
 	}
 
-	private boolean isBetween(Comparable<T> comparable) {
+	private boolean isBetween(@Nullable Comparable<T> comparable) {
 		T lowerBound = operands.lowerBound.get();
 		T upperBound = operands.upperBound.get();
 		if (lowerBound == null && upperBound == null) {
@@ -335,7 +337,7 @@ private boolean isBetween(Comparable<T> comparable) {
 		return lowerCompareResult >= 0 && upperCompareResult <= 0;
 	}
 
-	private boolean isNotBetweenExclusive(Comparable<T> comparable) {
+	private boolean isNotBetweenExclusive(@Nullable Comparable<T> comparable) {
 		T lowerBound = operands.lowerBound.get();
 		T upperBound = operands.upperBound.get();
 		if (lowerBound == null && upperBound == null) {
@@ -360,7 +362,7 @@ private boolean isNotBetweenExclusive(Comparable<T> comparable) {
 		return lowerCompareResult < 0 || upperCompareResult > 0;
 	}
 
-	private boolean isNotBetween(Comparable<T> comparable) {
+	private boolean isNotBetween(@Nullable Comparable<T> comparable) {
 		T lowerBound = operands.lowerBound.get();
 		T upperBound = operands.upperBound.get();
 		if (lowerBound == null && upperBound == null) {
@@ -385,11 +387,11 @@ private boolean isNotBetween(Comparable<T> comparable) {
 		return lowerCompareResult <= 0 || upperCompareResult >= 0;
 	}
 
-	private boolean isIn(Comparable<T> comparable) {
+	private boolean isIn(@Nullable Comparable<T> comparable) {
 		return operands.in.get().contains(comparable);
 	}
 
-	private boolean isNotIn(Comparable<T> comparable) {
+	private boolean isNotIn(@Nullable Comparable<T> comparable) {
 		return !isIn(comparable);
 	}
 
@@ -399,13 +401,13 @@ private void checkLock() {
 		}
 	}
 
-	private void validateOperator(Operator operator) {
+	private void validateOperator(@Nullable Operator operator) {
 		if (operators != null && !operators.contains(requireNonNull(operator))) {
 			throw new IllegalArgumentException("Operator " + operator + " not available");
 		}
 	}
 
-	private static <T> T stringOrCharacterToLowerCase(T value) {
+	private static <T> @Nullable T stringOrCharacterToLowerCase(@Nullable T value) {
 		if (value instanceof String) {
 			return (T) ((String) value).toLowerCase();
 		}
@@ -416,7 +418,7 @@ private static <T> T stringOrCharacterToLowerCase(T value) {
 		return value;
 	}
 
-	private static <T> Comparable<T> stringOrCharacterToLowerCase(Comparable<T> comparable) {
+	private static <T> @Nullable Comparable<T> stringOrCharacterToLowerCase(@Nullable Comparable<T> comparable) {
 		if (comparable instanceof String) {
 			return (Comparable<T>) ((String) comparable).toLowerCase();
 		}
@@ -432,7 +434,7 @@ private final class AutoEnableListener implements Runnable {
 		@Override
 		public void run() {
 			if (autoEnable.get()) {
-				switch (operator.get()) {
+				switch (operator.getOrThrow()) {
 					case EQUAL:
 					case NOT_EQUAL:
 						enabled.set(operands.equal.isNotNull());
@@ -513,7 +515,7 @@ private static final class EqualOperand<T> extends AbstractValue<T> {
 			private final Value<Wildcard> wildcard;
 			private final ValueObserver<Operator> operatorObserver;
 
-			private T value;
+			private @Nullable T value;
 
 			private EqualOperand(Wildcard wildcard, ValueObserver<Operator> operatorObserver) {
 				super(null, Notify.WHEN_SET);
@@ -524,7 +526,7 @@ private EqualOperand(Wildcard wildcard, ValueObserver<Operator> operatorObserver
 			}
 
 			@Override
-			protected T getValue() {
+			protected @Nullable T getValue() {
 				return addWildcard(value);
 			}
 
@@ -533,11 +535,11 @@ protected void setValue(T value) {
 				this.value = value;
 			}
 
-			private T addWildcard(T operand) {
+			private @Nullable T addWildcard(@Nullable T operand) {
 				if (!(operand instanceof String)) {
 					return operand;
 				}
-				switch (operatorObserver.get()) {
+				switch (operatorObserver.getOrThrow()) {
 					//wildcard only used for EQUAL and NOT_EQUAL
 					case EQUAL:
 					case NOT_EQUAL:
@@ -549,7 +551,7 @@ private T addWildcard(T operand) {
 
 			private String addWildcard(String operand) {
 				String operandWithWildcards = operand;
-				switch (wildcard.get()) {
+				switch (wildcard.getOrThrow()) {
 					case PREFIX:
 						operandWithWildcards = addWildcardPrefix(operandWithWildcards);
 						break;
@@ -593,15 +595,15 @@ static final class DefaultBuilder<T> implements Builder<T> {
 
 		private List<Operator> operators;
 		private Operator operator = Operator.EQUAL;
-		private Format format;
-		private String dateTimePattern = LocaleDateTimePattern.builder()
+		private @Nullable Format format;
+		private @Nullable String dateTimePattern = LocaleDateTimePattern.builder()
 						.delimiterDash()
 						.yearFourDigits()
 						.hoursMinutesSeconds()
 						.build()
 						.dateTimePattern();
-		private Wildcard wildcard = WILDCARD.get();
-		private boolean caseSensitive = CASE_SENSITIVE.get();
+		private Wildcard wildcard = WILDCARD.getOrThrow();
+		private boolean caseSensitive = CASE_SENSITIVE.getOrThrow();
 		private boolean autoEnable = true;
 
 		DefaultBuilder(Class<T> valueClass) {
@@ -627,13 +629,13 @@ public Builder<T> operator(Operator operator) {
 		}
 
 		@Override
-		public Builder<T> format(Format format) {
+		public Builder<T> format(@Nullable Format format) {
 			this.format = format;
 			return this;
 		}
 
 		@Override
-		public Builder<T> dateTimePattern(String dateTimePattern) {
+		public Builder<T> dateTimePattern(@Nullable String dateTimePattern) {
 			this.dateTimePattern = dateTimePattern;
 			return this;
 		}
diff --git a/common/model/src/main/java/is/codion/common/model/condition/package-info.java b/common/model/src/main/java/is/codion/common/model/condition/package-info.java
index c56edb33dc..83cc2a9036 100644
--- a/common/model/src/main/java/is/codion/common/model/condition/package-info.java
+++ b/common/model/src/main/java/is/codion/common/model/condition/package-info.java
@@ -17,10 +17,12 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>Condition related classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.model.condition.ConditionModel#WILDCARD}
  * <li>{@link is.codion.common.model.condition.ConditionModel#CASE_SENSITIVE}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common.model.condition;
\ No newline at end of file
diff --git a/common/model/src/main/java/is/codion/common/model/package-info.java b/common/model/src/main/java/is/codion/common/model/package-info.java
new file mode 100644
index 0000000000..e9181a4bcd
--- /dev/null
+++ b/common/model/src/main/java/is/codion/common/model/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Application model related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.model;
\ No newline at end of file
diff --git a/common/model/src/main/java/is/codion/common/model/selection/package-info.java b/common/model/src/main/java/is/codion/common/model/selection/package-info.java
new file mode 100644
index 0000000000..4c9973cf61
--- /dev/null
+++ b/common/model/src/main/java/is/codion/common/model/selection/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Selection related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.model.selection;
\ No newline at end of file
diff --git a/common/model/src/main/java/is/codion/common/model/summary/ColumnSummary.java b/common/model/src/main/java/is/codion/common/model/summary/ColumnSummary.java
index e33d46b173..4dc0a0529c 100644
--- a/common/model/src/main/java/is/codion/common/model/summary/ColumnSummary.java
+++ b/common/model/src/main/java/is/codion/common/model/summary/ColumnSummary.java
@@ -26,6 +26,7 @@
 import java.util.OptionalDouble;
 
 import static is.codion.common.resource.MessageBundle.messageBundle;
+import static java.util.Objects.requireNonNull;
 import static java.util.ResourceBundle.getBundle;
 
 /**
@@ -57,7 +58,7 @@ public String toString() {
 
 		@Override
 		public <T extends Number> String summary(SummaryValues<T> summaryValues) {
-			Collection<T> values = summaryValues.values();
+			Collection<T> values = requireNonNull(summaryValues).values();
 			if (!values.isEmpty()) {
 				return addSubsetIndicator(summaryValues.format(values.stream()
 								.filter(Objects::nonNull)
@@ -78,7 +79,7 @@ public String toString() {
 
 		@Override
 		public <T extends Number> String summary(SummaryValues<T> summaryValues) {
-			Collection<T> values = summaryValues.values();
+			Collection<T> values = requireNonNull(summaryValues).values();
 			if (!values.isEmpty()) {
 				OptionalDouble average = values.stream()
 								.mapToDouble(value -> value == null ? 0d : value.doubleValue())
@@ -102,7 +103,7 @@ public String toString() {
 
 		@Override
 		public <T extends Number> String summary(SummaryValues<T> summaryValues) {
-			Collection<T> values = summaryValues.values();
+			Collection<T> values = requireNonNull(summaryValues).values();
 			if (!values.isEmpty()) {
 				OptionalDouble min = values.stream()
 								.filter(Objects::nonNull)
@@ -127,7 +128,7 @@ public String toString() {
 
 		@Override
 		public <T extends Number> String summary(SummaryValues<T> summaryValues) {
-			Collection<T> values = summaryValues.values();
+			Collection<T> values = requireNonNull(summaryValues).values();
 			if (!values.isEmpty()) {
 				OptionalDouble max = values.stream()
 								.filter(Objects::nonNull)
@@ -152,7 +153,7 @@ public String toString() {
 
 		@Override
 		public <T extends Number> String summary(SummaryValues<T> summaryValues) {
-			Collection<T> values = summaryValues.values();
+			Collection<T> values = requireNonNull(summaryValues).values();
 			if (!values.isEmpty()) {
 				OptionalDouble min = values.stream()
 								.filter(Objects::nonNull)
diff --git a/common/model/src/main/java/is/codion/common/model/summary/DefaultSummaryModel.java b/common/model/src/main/java/is/codion/common/model/summary/DefaultSummaryModel.java
index 9703a4602b..b61b18ad32 100644
--- a/common/model/src/main/java/is/codion/common/model/summary/DefaultSummaryModel.java
+++ b/common/model/src/main/java/is/codion/common/model/summary/DefaultSummaryModel.java
@@ -73,6 +73,6 @@ public ValueObserver<String> summaryText() {
 	}
 
 	private void updateSummary() {
-		summaryText.set(summary().get().summary(summaryValues));
+		summaryText.set(summary().getOrThrow().summary(summaryValues));
 	}
 }
diff --git a/common/model/src/main/java/is/codion/common/model/summary/DefaultTableSummaryModel.java b/common/model/src/main/java/is/codion/common/model/summary/DefaultTableSummaryModel.java
index 1676e7de53..c2adff0667 100644
--- a/common/model/src/main/java/is/codion/common/model/summary/DefaultTableSummaryModel.java
+++ b/common/model/src/main/java/is/codion/common/model/summary/DefaultTableSummaryModel.java
@@ -39,7 +39,7 @@ final class DefaultTableSummaryModel<C> implements TableSummaryModel<C> {
 
 	@Override
 	public Optional<SummaryModel> summaryModel(C identifier) {
-		return Optional.ofNullable(summaryModels.computeIfAbsent(identifier, k ->
+		return Optional.ofNullable(summaryModels.computeIfAbsent(requireNonNull(identifier), k ->
 						createSummaryModel(k, NumberFormat.getInstance()).orElse(null)));
 	}
 
diff --git a/common/model/src/main/java/is/codion/common/model/summary/package-info.java b/common/model/src/main/java/is/codion/common/model/summary/package-info.java
new file mode 100644
index 0000000000..77204e92a7
--- /dev/null
+++ b/common/model/src/main/java/is/codion/common/model/summary/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>Summary related classes.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.model.summary;
\ No newline at end of file
diff --git a/common/model/src/main/java/module-info.java b/common/model/src/main/java/module-info.java
index 9c11a3cb6a..b9e0d0f5a2 100644
--- a/common/model/src/main/java/module-info.java
+++ b/common/model/src/main/java/module-info.java
@@ -17,7 +17,7 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Shared model classes, such as:
+ * <p>Shared model classes.
  * <ul>
  * <li>{@link is.codion.common.model.UserPreferences}
  * <li>{@link is.codion.common.model.CancelException}
@@ -30,7 +30,9 @@
  * <li>{@link is.codion.common.model.summary.TableSummaryModel}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 module is.codion.common.model {
+	requires transitive org.jspecify;
 	requires java.prefs;
 	requires transitive is.codion.common.core;
 
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/client/Clients.java b/common/rmi/src/main/java/is/codion/common/rmi/client/Clients.java
index d80d90989f..cb6c427346 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/client/Clients.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/client/Clients.java
@@ -32,8 +32,6 @@
 import java.nio.file.Files;
 import java.security.KeyStore;
 
-import static is.codion.common.Text.nullOrEmpty;
-
 /**
  * Utility methods for remote clients
  */
@@ -95,7 +93,7 @@ private Clients() {}
 	 */
 	public static void resolveTrustStore() {
 		String trustStorePath = TRUSTSTORE.get();
-		if (nullOrEmpty(trustStorePath)) {
+		if (trustStorePath == null || trustStorePath.isEmpty()) {
 			LOG.warn("No truststore specified via {}", TRUSTSTORE.propertyName());
 			return;
 		}
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/client/ConnectionRequest.java b/common/rmi/src/main/java/is/codion/common/rmi/client/ConnectionRequest.java
index 6f59bdf0cd..719ac0aced 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/client/ConnectionRequest.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/client/ConnectionRequest.java
@@ -21,6 +21,8 @@
 import is.codion.common.user.User;
 import is.codion.common.version.Version;
 
+import org.jspecify.annotations.Nullable;
+
 import java.time.ZoneId;
 import java.util.Locale;
 import java.util.Map;
@@ -111,7 +113,7 @@ interface Builder {
 		 * @param clientVersion the client version
 		 * @return this Builder instance
 		 */
-		Builder clientVersion(Version clientVersion);
+		Builder clientVersion(@Nullable Version clientVersion);
 
 		/**
 		 * @param key the key
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/client/DefaultConnectionRequest.java b/common/rmi/src/main/java/is/codion/common/rmi/client/DefaultConnectionRequest.java
index 98b458eb1d..d017ba0ded 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/client/DefaultConnectionRequest.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/client/DefaultConnectionRequest.java
@@ -21,6 +21,8 @@
 import is.codion.common.user.User;
 import is.codion.common.version.Version;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.Serial;
 import java.io.Serializable;
 import java.time.ZoneId;
@@ -44,9 +46,9 @@ final class DefaultConnectionRequest implements ConnectionRequest, Serializable
 	private final String clientType;
 	private final Locale clientLocale = Locale.getDefault();
 	private final ZoneId clientTimeZone = ZoneId.systemDefault();
-	private final Version clientVersion;
+	private final @Nullable Version clientVersion;
 	private final Version frameworkVersion = Version.version();
-	private final Map<String, Object> parameters;
+	private final @Nullable Map<String, Object> parameters;
 
 	private DefaultConnectionRequest(DefaultBuilder builder) {
 		this.user = requireNonNull(builder.user, "user must be specified");
@@ -127,11 +129,11 @@ public String toString() {
 
 	static final class DefaultBuilder implements Builder {
 
-		private User user;
-		private UUID clientId;
-		private String clientType;
-		private Version clientVersion;
-		private Map<String, Object> parameters;
+		private @Nullable User user;
+		private @Nullable UUID clientId;
+		private @Nullable String clientType;
+		private @Nullable Version clientVersion;
+		private @Nullable Map<String, Object> parameters;
 
 		DefaultBuilder() {}
 
@@ -154,13 +156,14 @@ public Builder clientType(String clientType) {
 		}
 
 		@Override
-		public Builder clientVersion(Version clientVersion) {
+		public Builder clientVersion(@Nullable Version clientVersion) {
 			this.clientVersion = clientVersion;
 			return this;
 		}
 
 		@Override
 		public Builder parameter(String key, Object value) {
+			requireNonNull(key);
 			if (parameters == null) {
 				parameters = new HashMap<>();
 			}
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/client/package-info.java b/common/rmi/src/main/java/is/codion/common/rmi/client/package-info.java
index b19bac978e..662b07fffe 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/client/package-info.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/client/package-info.java
@@ -17,11 +17,13 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>RMI client related classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.rmi.client.Clients#SERVER_HOSTNAME}
  * <li>{@link is.codion.common.rmi.client.Clients#TRUSTSTORE}
  * <li>{@link is.codion.common.rmi.client.Clients#TRUSTSTORE_PASSWORD}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common.rmi.client;
\ No newline at end of file
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/AbstractServer.java b/common/rmi/src/main/java/is/codion/common/rmi/server/AbstractServer.java
index 6a0d1538b0..e464651812 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/server/AbstractServer.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/AbstractServer.java
@@ -26,6 +26,7 @@
 import is.codion.common.scheduler.TaskScheduler;
 import is.codion.common.user.User;
 
+import org.jspecify.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -77,8 +78,8 @@ public abstract class AbstractServer<T extends Remote, A extends ServerAdmin> ex
 	private volatile int connectionLimit = -1;
 	private volatile boolean shuttingDown = false;
 
-	private Registry registry;
-	private A admin;
+	private @Nullable Registry registry;
+	private @Nullable A admin;
 
 	/**
 	 * Instantiates a new AbstractServer
@@ -155,7 +156,7 @@ public final void setConnectionLimit(int connectionLimit) {
 	 * @return the maintenance check interval in ms
 	 */
 	public final int getMaintenanceInterval() {
-		return connectionMaintenanceScheduler.interval().get();
+		return connectionMaintenanceScheduler.interval().getOrThrow();
 	}
 
 	/**
@@ -296,6 +297,7 @@ final Collection<RemoteClient> clients(User user) {
 	 * @throws IllegalStateException in case an admin instance has already been set
 	 */
 	protected final void setAdmin(A admin) {
+		requireNonNull(admin);
 		if (this.admin != null) {
 			throw new IllegalStateException("Admin has already been set for this server");
 		}
@@ -502,7 +504,7 @@ private static void stopAuxiliaryServer(AuxiliaryServer server) {
 		}
 	}
 
-	private static void unexportSilently(Remote... remotes) {
+	private static void unexportSilently(@Nullable Remote... remotes) {
 		for (Remote remote : remotes) {
 			if (remote != null) {
 				try {
@@ -515,7 +517,7 @@ private static void unexportSilently(Remote... remotes) {
 		}
 	}
 
-	private static String clientHost(String requestParameterHost) {
+	private static String clientHost(@Nullable String requestParameterHost) {
 		if (requestParameterHost == null) {
 			try {
 				return getClientHost();
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerConfiguration.java b/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerConfiguration.java
index d69df9233d..f5aff05b66 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerConfiguration.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerConfiguration.java
@@ -20,6 +20,7 @@
 
 import is.codion.common.version.Version;
 
+import org.jspecify.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -54,9 +55,9 @@ final class DefaultServerConfiguration implements ServerConfiguration {
 	private final int adminPort;
 	private final boolean sslEnabled;
 	private final Supplier<String> serverNameSupplier;
-	private final RMIClientSocketFactory rmiClientSocketFactory;
-	private final RMIServerSocketFactory rmiServerSocketFactory;
-	private final String objectInputFilterFactoryClassName;
+	private final @Nullable RMIClientSocketFactory rmiClientSocketFactory;
+	private final @Nullable RMIServerSocketFactory rmiServerSocketFactory;
+	private final @Nullable String objectInputFilterFactoryClassName;
 	private final int connectionMaintenanceInterval;
 	private final int connectionLimit;
 
@@ -146,9 +147,9 @@ static final class DefaultBuilder implements Builder<DefaultBuilder> {
 		private int serverAdminPort;
 		private boolean sslEnabled = true;
 		private Supplier<String> serverName = new DefaultServerName();
-		private RMIClientSocketFactory rmiClientSocketFactory = new SslRMIClientSocketFactory();
-		private RMIServerSocketFactory rmiServerSocketFactory = new SslRMIServerSocketFactory();
-		private String objectInputFilterFactoryClassName;
+		private @Nullable RMIClientSocketFactory rmiClientSocketFactory = new SslRMIClientSocketFactory();
+		private @Nullable RMIServerSocketFactory rmiServerSocketFactory = new SslRMIServerSocketFactory();
+		private @Nullable String objectInputFilterFactoryClassName = OBJECT_INPUT_FILTER_FACTORY_CLASS_NAME.get();
 		private Integer connectionMaintenanceInterval = DEFAULT_CONNECTION_MAINTENANCE_INTERVAL;
 		private int connectionLimit = -1;
 
@@ -199,7 +200,7 @@ public DefaultBuilder sslEnabled(boolean sslEnabled) {
 		}
 
 		@Override
-		public DefaultBuilder objectInputFilterFactoryClassName(String objectInputFilterFactoryClassName) {
+		public DefaultBuilder objectInputFilterFactoryClassName(@Nullable String objectInputFilterFactoryClassName) {
 			this.objectInputFilterFactoryClassName = objectInputFilterFactoryClassName;
 			return this;
 		}
@@ -266,7 +267,7 @@ private static final class DefaultServerName implements Supplier<String> {
 
 		@Override
 		public String get() {
-			String serverNamePrefix = SERVER_NAME_PREFIX.get();
+			String serverNamePrefix = SERVER_NAME_PREFIX.getOrThrow();
 			if (serverNamePrefix.isEmpty()) {
 				throw new IllegalArgumentException("serverNamePrefix must not be empty");
 			}
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerLocator.java b/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerLocator.java
index 9b36295f66..f3aae74474 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerLocator.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/DefaultServerLocator.java
@@ -18,6 +18,7 @@
  */
 package is.codion.common.rmi.server;
 
+import org.jspecify.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -108,8 +109,8 @@ private static <T extends Remote, A extends ServerAdmin> void addIfReachable(Str
 		}
 	}
 
-	private static <T extends Remote, A extends ServerAdmin> Server<T, A> getIfReachable(Server<T, A> server,
-																																											 int requestedServerPort) throws RemoteException {
+	private static <T extends Remote, A extends ServerAdmin> @Nullable Server<T, A> getIfReachable(Server<T, A> server,
+																																																 int requestedServerPort) throws RemoteException {
 		ServerInformation serverInformation = server.serverInformation();
 		if (requestedServerPort != -1 && serverInformation.serverPort() != requestedServerPort) {
 			LOG.warn("Server \"{}\" is serving on port {}, requested port was {}",
@@ -126,10 +127,10 @@ private static <T extends Remote, A extends ServerAdmin> Server<T, A> getIfReach
 
 	static final class DefaultBuilder implements Server.Locator.Builder {
 
-		private String hostName = ServerConfiguration.RMI_SERVER_HOSTNAME.get();
-		private String namePrefix = ServerConfiguration.SERVER_NAME_PREFIX.get();
-		private int registryPort = ServerConfiguration.REGISTRY_PORT.get();
-		private int port = ServerConfiguration.SERVER_PORT.get();
+		private String hostName = ServerConfiguration.RMI_SERVER_HOSTNAME.getOrThrow();
+		private String namePrefix = ServerConfiguration.SERVER_NAME_PREFIX.getOrThrow();
+		private int registryPort = ServerConfiguration.REGISTRY_PORT.getOrThrow();
+		private int port = ServerConfiguration.SERVER_PORT.getOrThrow();
 
 		@Override
 		public Builder hostName(String hostName) {
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/ServerConfiguration.java b/common/rmi/src/main/java/is/codion/common/rmi/server/ServerConfiguration.java
index 693856fc48..80f29e124a 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/server/ServerConfiguration.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/ServerConfiguration.java
@@ -22,6 +22,8 @@
 import is.codion.common.Text;
 import is.codion.common.property.PropertyValue;
 
+import org.jspecify.annotations.Nullable;
+
 import java.rmi.registry.Registry;
 import java.rmi.server.RMIClientSocketFactory;
 import java.rmi.server.RMIServerSocketFactory;
@@ -296,7 +298,7 @@ interface Builder<B extends Builder<B>> {
 		 * @param objectInputFilterFactoryClassName the object input filter factory class name
 		 * @return this builder instance
 		 */
-		B objectInputFilterFactoryClassName(String objectInputFilterFactoryClassName);
+		B objectInputFilterFactoryClassName(@Nullable String objectInputFilterFactoryClassName);
 
 		/**
 		 * @param connectionMaintenanceInterval the interval between server connection maintenance runs, in milliseconds.
@@ -342,10 +344,9 @@ static <B extends Builder<B>> Builder<B> builder(int serverPort, int registryPor
 	 */
 	static <B extends Builder<B>> Builder<B> builderFromSystemProperties() {
 		return (Builder<B>) builder(SERVER_PORT.getOrThrow(), REGISTRY_PORT.getOrThrow())
-						.auxiliaryServerFactoryClassNames(Text.parseCommaSeparatedValues(AUXILIARY_SERVER_FACTORY_CLASS_NAMES.get()))
-						.adminPort(ADMIN_PORT.get())
-						.sslEnabled(SSL_ENABLED.get())
-						.connectionMaintenanceInterval(CONNECTION_MAINTENANCE_INTERVAL.get())
-						.objectInputFilterFactoryClassName(OBJECT_INPUT_FILTER_FACTORY_CLASS_NAME.get());
+						.auxiliaryServerFactoryClassNames(Text.parseCommaSeparatedValues(AUXILIARY_SERVER_FACTORY_CLASS_NAMES.getOrThrow()))
+						.adminPort(ADMIN_PORT.getOrThrow())
+						.sslEnabled(SSL_ENABLED.getOrThrow())
+						.connectionMaintenanceInterval(CONNECTION_MAINTENANCE_INTERVAL.getOrThrow());
 	}
 }
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/WhitelistInputFilterFactory.java b/common/rmi/src/main/java/is/codion/common/rmi/server/WhitelistInputFilterFactory.java
index dabc03f840..95a960adb0 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/server/WhitelistInputFilterFactory.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/WhitelistInputFilterFactory.java
@@ -42,7 +42,7 @@ public final class WhitelistInputFilterFactory implements ObjectInputFilterFacto
 	@Override
 	public ObjectInputFilter createObjectInputFilter() {
 		String whitelist = SERIALIZATION_FILTER_WHITELIST.getOrThrow();
-		if (SERIALIZATION_FILTER_DRYRUN.get()) {
+		if (SERIALIZATION_FILTER_DRYRUN.getOrThrow()) {
 			return SerializationWhitelist.whitelistDryRun(whitelist);
 		}
 
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/exception/package-info.java b/common/rmi/src/main/java/is/codion/common/rmi/server/exception/package-info.java
new file mode 100644
index 0000000000..b71046461c
--- /dev/null
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/exception/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * This file is part of Codion.
+ *
+ * Codion is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Codion is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Codion.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
+ */
+/**
+ * <p>RMI server related exceptions.
+ */
+@org.jspecify.annotations.NullMarked
+package is.codion.common.rmi.server.exception;
\ No newline at end of file
diff --git a/common/rmi/src/main/java/is/codion/common/rmi/server/package-info.java b/common/rmi/src/main/java/is/codion/common/rmi/server/package-info.java
index 8649ea5af7..3bd99022ec 100644
--- a/common/rmi/src/main/java/is/codion/common/rmi/server/package-info.java
+++ b/common/rmi/src/main/java/is/codion/common/rmi/server/package-info.java
@@ -17,7 +17,8 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * Package configuration values:
+ * <p>RMI server related classes.
+ * <p>Package configuration values:
  * <ul>
  * <li>{@link is.codion.common.rmi.server.ServerConfiguration#RMI_SERVER_HOSTNAME}
  * <li>{@link is.codion.common.rmi.server.ServerConfiguration#SERVER_NAME_PREFIX}
@@ -35,4 +36,5 @@
  * <li>{@link is.codion.common.rmi.server.WhitelistInputFilterFactory#SERIALIZATION_FILTER_DRYRUN}
  * </ul>
  */
+@org.jspecify.annotations.NullMarked
 package is.codion.common.rmi.server;
\ No newline at end of file
diff --git a/common/rmi/src/main/java/module-info.java b/common/rmi/src/main/java/module-info.java
index 9520f9e61b..b25a14be2d 100644
--- a/common/rmi/src/main/java/module-info.java
+++ b/common/rmi/src/main/java/module-info.java
@@ -17,7 +17,7 @@
  * Copyright (c) 2023 - 2024, Björn Darri Sigurðsson.
  */
 /**
- * RMI client/server classes, such as:
+ * <p>RMI client/server classes.
  * <ul>
  * <li>{@link is.codion.common.rmi.client.ConnectionRequest}
  * <li>{@link is.codion.common.rmi.server.Server}
@@ -31,7 +31,9 @@
  * @uses is.codion.common.rmi.server.ObjectInputFilterFactory
  * @provides is.codion.common.rmi.server.ObjectInputFilterFactory
  */
+@org.jspecify.annotations.NullMarked
 module is.codion.common.rmi {
+	requires transitive org.jspecify;
 	requires org.slf4j;
 	requires jdk.management;
 	requires nl.altindag.ssl;
diff --git a/framework/server/src/main/java/is/codion/framework/server/DefaultEntityServerConfiguration.java b/framework/server/src/main/java/is/codion/framework/server/DefaultEntityServerConfiguration.java
index 81e7ecdd75..8197f02a65 100644
--- a/framework/server/src/main/java/is/codion/framework/server/DefaultEntityServerConfiguration.java
+++ b/framework/server/src/main/java/is/codion/framework/server/DefaultEntityServerConfiguration.java
@@ -170,17 +170,14 @@ public Map<String, Integer> clientTypeIdleConnectionTimeouts() {
 	static EntityServerConfiguration.Builder builderFromSystemProperties() {
 		Builder builder = new DefaultBuilder(SERVER_PORT.getOrThrow(), REGISTRY_PORT.getOrThrow())
 						.auxiliaryServerFactoryClassNames(Text.parseCommaSeparatedValues(AUXILIARY_SERVER_FACTORY_CLASS_NAMES.get()))
-						.sslEnabled(SSL_ENABLED.get())
-						.objectInputFilterFactoryClassName(OBJECT_INPUT_FILTER_FACTORY_CLASS_NAME.get())
+						.sslEnabled(SSL_ENABLED.getOrThrow())
 						.adminPort(ADMIN_PORT.getOrThrow())
-						.connectionLimit(CONNECTION_LIMIT.get())
+						.connectionLimit(CONNECTION_LIMIT.getOrThrow())
 						.database(Database.instance())
 						.domainClassNames(Text.parseCommaSeparatedValues(DOMAIN_MODEL_CLASSES.get()))
 						.connectionPoolUsers(Text.parseCommaSeparatedValues(CONNECTION_POOL_USERS.get()).stream()
 										.map(User::parse)
-										.collect(toList()))
-						.clientLogging(CLIENT_LOGGING.get())
-						.idleConnectionTimeout(IDLE_CONNECTION_TIMEOUT.get());
+										.collect(toList()));
 		Map<String, Integer> clientTypeIdleConnectionTimeoutMap = new HashMap<>();
 		for (String clientTimeout : Text.parseCommaSeparatedValues(CLIENT_CONNECTION_TIMEOUT.get())) {
 			String[] split = clientTimeout.split(":");
@@ -209,8 +206,8 @@ static final class DefaultBuilder implements Builder {
 
 		private Database database;
 		private User adminUser;
-		private boolean clientLogging = CLIENT_LOGGING.get();
-		private int idleConnectionTimeout = IDLE_CONNECTION_TIMEOUT.get();
+		private boolean clientLogging = CLIENT_LOGGING.getOrThrow();
+		private int idleConnectionTimeout = IDLE_CONNECTION_TIMEOUT.getOrThrow();
 		private String connectionPoolFactory;
 		private final Collection<String> domainClassNames = new HashSet<>();
 		private final Collection<User> connectionPoolUsers = new HashSet<>();
@@ -223,7 +220,7 @@ static final class DefaultBuilder implements Builder {
 					throw new IllegalStateException("Database must be set before initializing server name");
 				}
 
-				String serverNamePrefix = SERVER_NAME_PREFIX.get();
+				String serverNamePrefix = SERVER_NAME_PREFIX.getOrThrow();
 				if (serverNamePrefix.isEmpty()) {
 					throw new IllegalArgumentException("serverNamePrefix must not be empty");
 				}
diff --git a/settings.gradle b/settings.gradle
index 2124d54bec..e5150e2702 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -201,6 +201,7 @@ dependencyResolutionManagement {
             version("tomcat", "11.0.2")
 
             version("jasperreports", "7.0.1")
+            version("jspecify", "1.0.0")
 
             library("slf4j-api", "org.slf4j", "slf4j-api").versionRef("slf4j.api")
             library("logback-core", "ch.qos.logback", "logback-core").versionRef("logback")
@@ -231,6 +232,8 @@ dependencyResolutionManagement {
             library("log4j-core", "org.apache.logging.log4j", "log4j-core").versionRef("log4j")
             library("tomcat-jdbc", "org.apache.tomcat", "tomcat-jdbc").versionRef("tomcat")
 
+            library("jspecify", "org.jspecify", "jspecify").versionRef("jspecify")
+
             library("jasperreports", "net.sf.jasperreports", "jasperreports").versionRef("jasperreports")
             library("jasperreports-jdt", "net.sf.jasperreports", "jasperreports-jdt").versionRef("jasperreports")
         }