Apply NullAway

Motivation:

Before adopting NullAway(line#1680) or other static analysis tools.
Manually run it and clean up errors.

Modifications:

- Fix all true positives reported by NullAway

Result:

Less NullAway errors

build.gradle

@@ -2,7 +2,7 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
     id 'com.google.osdetector' version '1.6.2' apply false
-    // If you want to change `org.jetbrains.kotlin.jvm` version, 
+    // If you want to change `org.jetbrains.kotlin.jvm` version,
     // you also need to change `org.jetbrains.kotlin:kotlin-allopen` version in `dependencies.yml`.
     id 'org.jetbrains.kotlin.jvm' version '1.3.72' apply false
 }

core/src/main/java/com/linecorp/armeria/client/Client.java

@@ -18,6 +18,8 @@
 
 import static java.util.Objects.requireNonNull;
 
+import javax.annotation.Nullable;
+
 import com.linecorp.armeria.common.HttpRequest;
 import com.linecorp.armeria.common.HttpResponse;
 import com.linecorp.armeria.common.Request;
@@ -71,6 +73,7 @@ public interface Client<I extends Request, O extends Response> extends Unwrappab
      * @see ClientFactory#unwrap(Object, Class)
      * @see Unwrappable
      */
+    @Nullable
     @Override
     default <T> T as(Class<T> type) {
         requireNonNull(type, "type");

core/src/main/java/com/linecorp/armeria/client/ClientRequestContextWrapper.java

@@ -49,16 +49,19 @@ public ClientRequestContext newDerivedContext(RequestId id, @Nullable HttpReques
         return delegate().newDerivedContext(id, req, rpcReq, endpoint);
     }
 
+    @Nullable
     @Override
     public EndpointGroup endpointGroup() {
         return delegate().endpointGroup();
     }
 
+    @Nullable
     @Override
     public Endpoint endpoint() {
         return delegate().endpoint();
     }
 
+    @Nullable
     @Override
     public String fragment() {
         return delegate().fragment();

core/src/main/java/com/linecorp/armeria/client/DecoratingClientFactory.java

@@ -118,11 +118,13 @@ public Object newClient(ClientBuilderParams params) {
         return delegate().newClient(params);
     }
 
+    @Nullable
     @Override
     public <T> ClientBuilderParams clientBuilderParams(T client) {
         return delegate().clientBuilderParams(client);
     }
 
+    @Nullable
     @Override
     public <T> T unwrap(Object client, Class<T> type) {
         return delegate().unwrap(client, type);

core/src/main/java/com/linecorp/armeria/client/DefaultClientFactory.java

@@ -153,6 +153,7 @@ public Object newClient(ClientBuilderParams params) {
         return factory.newClient(params);
     }
 
+    @Nullable
     @Override
     public <T> T unwrap(Object client, Class<T> type) {
         final T params = ClientFactory.super.unwrap(client, type);

core/src/main/java/com/linecorp/armeria/client/DefaultClientRequestContext.java

@@ -393,11 +393,13 @@ public ClientOptions options() {
 
     @Override
     public EndpointGroup endpointGroup() {
+        checkState(endpointGroup != null, "Should call init(endpoint) before invoking this method.");
         return endpointGroup;
     }
 
     @Override
     public Endpoint endpoint() {
+        checkState(endpoint != null, "Should call init(endpoint) before invoking this method.");
         return endpoint;
     }
 

core/src/main/java/com/linecorp/armeria/client/HttpSessionHandler.java

@@ -122,6 +122,7 @@ final class HttpSessionHandler extends ChannelDuplexHandler implements HttpSessi
         this.pingIntervalMillis = pingIntervalMillis;
     }
 
+    @Nullable
     @Override
     public SessionProtocol protocol() {
         return protocol;

core/src/main/java/com/linecorp/armeria/client/RefreshingAddressResolver.java

@@ -327,7 +327,7 @@ public void run() {
                 servedFromCache = false;
                 numAttemptsSoFar = 1;
 
-                if (entry.address().equals(address) && entry.ttlMillis() == ttlMillis) {
+                if (address.equals(entry.address()) && entry.ttlMillis() == ttlMillis) {
                     scheduleRefresh(ttlMillis);
                 } else {
                     // Replace the old entry with the new one.

core/src/main/java/com/linecorp/armeria/client/circuitbreaker/NonBlockingCircuitBreaker.java

@@ -289,11 +289,13 @@ public EventCount count() {
             return EventCount.ZERO;
         }
 
+        @Nullable
         @Override
         public EventCount onSuccess() {
             return null;
         }
 
+        @Nullable
         @Override
         public EventCount onFailure() {
             return null;

core/src/main/java/com/linecorp/armeria/client/circuitbreaker/SlidingWindowCounter.java

@@ -67,11 +67,13 @@ public EventCount count() {
         return snapshot.get();
     }
 
+    @Nullable
     @Override
     public EventCount onSuccess() {
         return onEvent(Event.SUCCESS);
     }
 
+    @Nullable
     @Override
     public EventCount onFailure() {
         return onEvent(Event.FAILURE);

core/src/main/java/com/linecorp/armeria/client/endpoint/DynamicEndpointGroup.java

@@ -26,6 +26,8 @@
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
+import javax.annotation.Nullable;
+
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 
@@ -81,6 +83,7 @@ public final EndpointSelectionStrategy selectionStrategy() {
         return selectionStrategy;
     }
 
+    @Nullable
     @Override
     public final Endpoint select(ClientRequestContext ctx) {
         return maybeCreateSelector().select(ctx);

core/src/main/java/com/linecorp/armeria/client/endpoint/EndpointGroup.java

@@ -23,6 +23,8 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.function.Consumer;
 
+import javax.annotation.Nullable;
+
 import com.google.common.collect.ImmutableList;
 
 import com.linecorp.armeria.client.ClientRequestContext;
@@ -139,6 +141,7 @@ static EndpointGroup of(EndpointSelectionStrategy selectionStrategy,
      *         which was specified when constructing this {@link EndpointGroup},
      *         or {@code null} if this {@link EndpointGroup} is empty.
      */
+    @Nullable
     @Override
     Endpoint select(ClientRequestContext ctx);
 

core/src/main/java/com/linecorp/armeria/client/endpoint/OrElseEndpointGroup.java

@@ -21,6 +21,8 @@
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 
+import javax.annotation.Nullable;
+
 import com.linecorp.armeria.client.ClientRequestContext;
 import com.linecorp.armeria.client.Endpoint;
 import com.linecorp.armeria.common.util.AbstractListenable;
@@ -66,6 +68,7 @@ public EndpointSelectionStrategy selectionStrategy() {
         return first.selectionStrategy();
     }
 
+    @Nullable
     @Override
     public Endpoint select(ClientRequestContext ctx) {
         return selector.select(ctx);

core/src/main/java/com/linecorp/armeria/client/endpoint/RoundRobinStrategy.java

@@ -21,6 +21,8 @@
 import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import javax.annotation.Nullable;
+
 import com.linecorp.armeria.client.ClientRequestContext;
 import com.linecorp.armeria.client.Endpoint;
 
@@ -49,6 +51,7 @@ static class RoundRobinSelector implements EndpointSelector {
             this.endpointGroup = requireNonNull(endpointGroup, "endpointGroup");
         }
 
+        @Nullable
         @Override
         public Endpoint select(ClientRequestContext ctx) {
 

core/src/main/java/com/linecorp/armeria/client/endpoint/StaticEndpointGroup.java

@@ -20,6 +20,8 @@
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 
+import javax.annotation.Nullable;
+
 import com.google.common.collect.ImmutableList;
 
 import com.linecorp.armeria.client.ClientRequestContext;
@@ -57,6 +59,7 @@ public EndpointSelectionStrategy selectionStrategy() {
         return selectionStrategy;
     }
 
+    @Nullable
     @Override
     public Endpoint select(ClientRequestContext ctx) {
         return selector.select(ctx);

core/src/main/java/com/linecorp/armeria/client/endpoint/StickyEndpointSelectionStrategy.java

@@ -20,6 +20,8 @@
 import java.util.List;
 import java.util.function.ToLongFunction;
 
+import javax.annotation.Nullable;
+
 import com.google.common.hash.Hashing;
 
 import com.linecorp.armeria.client.ClientRequestContext;
@@ -80,6 +82,7 @@ private static final class StickyEndpointSelector implements EndpointSelector {
             this.endpointGroup = requireNonNull(endpointGroup, "endpointGroup");
         }
 
+        @Nullable
         @Override
         public Endpoint select(ClientRequestContext ctx) {
 

core/src/main/java/com/linecorp/armeria/client/endpoint/WeightedRoundRobinStrategy.java

@@ -61,6 +61,7 @@ private static final class WeightedRoundRobinSelector implements EndpointSelecto
             endpointGroup.addListener(endpoints -> endpointsAndWeights = new EndpointsAndWeights(endpoints));
         }
 
+        @Nullable
         @Override
         public Endpoint select(ClientRequestContext ctx) {
             final int currentSequence = sequence.getAndIncrement();

core/src/main/java/com/linecorp/armeria/client/retry/Backoff.java

@@ -23,6 +23,8 @@
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Supplier;
 
+import javax.annotation.Nullable;
+
 import com.linecorp.armeria.common.util.Unwrappable;
 
 /**
@@ -149,6 +151,7 @@ static Backoff of(String specification) {
      *
      * @see Unwrappable
      */
+    @Nullable
     @Override
     default <T> T as(Class<T> type) {
         return Unwrappable.super.as(type);

core/src/main/java/com/linecorp/armeria/common/DefaultAggregatedHttpRequest.java

@@ -47,11 +47,13 @@ public String path() {
         return headers.path();
     }
 
+    @Nullable
     @Override
     public String scheme() {
         return headers.scheme();
     }
 
+    @Nullable
     @Override
     public String authority() {
         return headers.authority();

core/src/main/java/com/linecorp/armeria/common/DefaultCookie.java

@@ -87,11 +87,13 @@ public boolean isValueQuoted() {
         return valueQuoted;
     }
 
+    @Nullable
     @Override
     public String domain() {
         return domain;
     }
 
+    @Nullable
     @Override
     public String path() {
         return path;
@@ -112,6 +114,7 @@ public boolean isHttpOnly() {
         return httpOnly;
     }
 
+    @Nullable
     @Override
     public String sameSite() {
         return sameSite;

core/src/main/java/com/linecorp/armeria/common/MediaType.java

@@ -1214,6 +1214,7 @@ private static final class KnownTypesByString {
                       .distinct()
                       .collect(toImmutableMap(MediaType::toString, Function.identity(), (a, b) -> a));
 
+        @Nullable
         static MediaType get(String input) {
             return KNOWN_TYPES_BY_STRING.get(input);
         }

core/src/main/java/com/linecorp/armeria/common/NonWrappingRequestContext.java

@@ -80,11 +80,13 @@ protected NonWrappingRequestContext(
         this.rpcReq = rpcReq;
     }
 
+    @Nullable
     @Override
     public HttpRequest request() {
         return req;
     }
 
+    @Nullable
     @Override
     public RpcRequest rpcRequest() {
         return rpcReq;
@@ -174,6 +176,7 @@ public final String decodedPath() {
         return this.decodedPath = ArmeriaHttpUtil.decodePath(path);
     }
 
+    @Nullable
     @Override
     public final String query() {
         return query;

core/src/main/java/com/linecorp/armeria/common/RequestContextWrapper.java

@@ -168,6 +168,7 @@ public String decodedPath() {
         return delegate().decodedPath();
     }
 
+    @Nullable
     @Override
     public String query() {
         return delegate().query();