diff --git a/src/Kook.Net.CardMarkup/CardMarkupSerializer.cs b/src/Kook.Net.CardMarkup/CardMarkupSerializer.cs
index a5fbb482..ee189c17 100644
--- a/src/Kook.Net.CardMarkup/CardMarkupSerializer.cs
+++ b/src/Kook.Net.CardMarkup/CardMarkupSerializer.cs
@@ -3,6 +3,10 @@
 using Kook.CardMarkup.Extensions;
 using Kook.CardMarkup.Models;
 
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+using System.Diagnostics.CodeAnalysis;
+#endif
+
 namespace Kook.CardMarkup;
 
 /// <summary>
@@ -242,7 +246,11 @@ public static IEnumerable<ICard> Deserialize(Stream xmlStream)
     /// <param name="file">UTF-8 encoded XML file</param>
     /// <param name="cards"><see cref="ICard"/> enumerable, will be null if return value is false</param>
     /// <returns>True if deserialization is successful, otherwise false</returns>
-    public static bool TryDeserialize(FileInfo file, out IEnumerable<ICard>? cards)
+    public static bool TryDeserialize(FileInfo file,
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+        [NotNullWhen(true)]
+#endif
+        out IEnumerable<ICard>? cards)
     {
         try
         {
@@ -262,7 +270,11 @@ public static bool TryDeserialize(FileInfo file, out IEnumerable<ICard>? cards)
     /// <param name="xmlText">UTF-8 encoded XML text</param>
     /// <param name="cards"><see cref="ICard"/> enumerable, will be null if return value is false</param>
     /// <returns>True if deserialization is successful, otherwise false</returns>
-    public static bool TryDeserialize(string xmlText, out IEnumerable<ICard>? cards)
+    public static bool TryDeserialize(string xmlText,
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+        [NotNullWhen(true)]
+#endif
+        out IEnumerable<ICard>? cards)
     {
         try
         {
@@ -282,7 +294,11 @@ public static bool TryDeserialize(string xmlText, out IEnumerable<ICard>? cards)
     /// <param name="xmlStream">UTF-8 encoded XML stream</param>
     /// <param name="cards"><see cref="ICard"/> enumerable, will be null if return value is false</param>
     /// <returns>True if deserialization is successful, otherwise false</returns>
-    public static bool TryDeserialize(Stream xmlStream, out IEnumerable<ICard>? cards)
+    public static bool TryDeserialize(Stream xmlStream,
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+        [NotNullWhen(true)]
+#endif
+        out IEnumerable<ICard>? cards)
     {
         try
         {
diff --git a/src/Kook.Net.Core/Extensions/CardExtensions.cs b/src/Kook.Net.Core/Extensions/CardExtensions.cs
index 3fff2c07..18b00c33 100644
--- a/src/Kook.Net.Core/Extensions/CardExtensions.cs
+++ b/src/Kook.Net.Core/Extensions/CardExtensions.cs
@@ -48,7 +48,10 @@ public static KMarkdownElementBuilder ToBuilder(this KMarkdownElement entity)
     public static ImageElementBuilder ToBuilder(this ImageElement entity)
     {
         if (entity is null) return null;
-        return new ImageElementBuilder { Source = entity.Source, Alternative = entity.Alternative, Size = entity.Size, Circle = entity.Circle };
+        return new ImageElementBuilder
+        {
+            Source = entity.Source, Alternative = entity.Alternative, Size = entity.Size, Circle = entity.Circle
+        };
     }
 
     /// <summary>
@@ -57,7 +60,10 @@ public static ImageElementBuilder ToBuilder(this ImageElement entity)
     public static ButtonElementBuilder ToBuilder(this ButtonElement entity)
     {
         if (entity is null) return null;
-        return new ButtonElementBuilder { Theme = entity.Theme, Click = entity.Click, Value = entity.Value, Text = entity.Text.ToBuilder() };
+        return new ButtonElementBuilder
+        {
+            Theme = entity.Theme, Click = entity.Click, Value = entity.Value, Text = entity.Text.ToBuilder()
+        };
     }
 
     /// <summary>
@@ -66,7 +72,10 @@ public static ButtonElementBuilder ToBuilder(this ButtonElement entity)
     public static ParagraphStructBuilder ToBuilder(this ParagraphStruct entity)
     {
         if (entity is null) return null;
-        return new ParagraphStructBuilder { ColumnCount = entity.ColumnCount, Fields = entity.Fields.Select(x => x.ToBuilder()).ToList() };
+        return new ParagraphStructBuilder
+        {
+            ColumnCount = entity.ColumnCount, Fields = entity.Fields.Select(x => x.ToBuilder()).ToList()
+        };
     }
 
     #endregion
@@ -112,7 +121,12 @@ public static HeaderModuleBuilder ToBuilder(this HeaderModule entity)
     public static SectionModuleBuilder ToBuilder(this SectionModule entity)
     {
         if (entity is null) return null;
-        return new SectionModuleBuilder { Mode = entity.Mode, Text = entity.Text.ToBuilder(), Accessory = entity.Accessory.ToBuilder() };
+        return new SectionModuleBuilder
+        {
+            Mode = entity.Mode,
+            Text = entity.Text.ToBuilder(),
+            Accessory = entity.Accessory.ToBuilder()
+        };
     }
 
     /// <summary>
@@ -193,7 +207,10 @@ public static VideoModuleBuilder ToBuilder(this VideoModule entity)
     public static CountdownModuleBuilder ToBuilder(this CountdownModule entity)
     {
         if (entity is null) return null;
-        return new CountdownModuleBuilder { Mode = entity.Mode, EndTime = entity.EndTime, StartTime = entity.StartTime };
+        return new CountdownModuleBuilder
+        {
+            Mode = entity.Mode, EndTime = entity.EndTime, StartTime = entity.StartTime
+        };
     }
 
     /// <summary>
@@ -232,7 +249,10 @@ public static CardBuilder ToBuilder(this Card builder)
 
         return new CardBuilder
         {
-            Theme = builder.Theme, Size = builder.Size, Color = builder.Color, Modules = builder.Modules.Select(m => m.ToBuilder()).ToList()
+            Theme = builder.Theme,
+            Size = builder.Size,
+            Color = builder.Color,
+            Modules = builder.Modules.Select(m => m.ToBuilder()).ToList()
         };
     }
 
diff --git a/src/Kook.Net.Rest/Extensions/CardJsonExtension.cs b/src/Kook.Net.Rest/Extensions/CardJsonExtension.cs
index 07d7453b..7ebae4da 100644
--- a/src/Kook.Net.Rest/Extensions/CardJsonExtension.cs
+++ b/src/Kook.Net.Rest/Extensions/CardJsonExtension.cs
@@ -4,6 +4,10 @@
 using Kook.API;
 using Kook.Net.Converters;
 
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+using System.Diagnostics.CodeAnalysis;
+#endif
+
 namespace Kook.Rest;
 
 /// <summary>
@@ -24,9 +28,12 @@ public static class CardJsonExtension
     /// <param name="json">The json string to parse.</param>
     /// <param name="builder">The <see cref="ICardBuilder"/> with populated values. An empty instance if method returns <c>false</c>.</param>
     /// <returns><c>true</c> if <paramref name="json"/> was successfully parsed. <c>false</c> if not.</returns>
-    public static bool TryParseSingle(string json, out ICardBuilder builder)
+    public static bool TryParseSingle(string json,
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+        [NotNullWhen(true)]
+#endif
+        out ICardBuilder builder)
     {
-        builder = new CardBuilder();
         try
         {
             CardBase model = JsonSerializer.Deserialize<CardBase>(json, _options.Value);
@@ -37,10 +44,12 @@ public static bool TryParseSingle(string json, out ICardBuilder builder)
                 return true;
             }
 
+            builder = new CardBuilder();
             return false;
         }
         catch
         {
+            builder = new CardBuilder();
             return false;
         }
     }
@@ -51,9 +60,12 @@ public static bool TryParseSingle(string json, out ICardBuilder builder)
     /// <param name="json">The json string to parse.</param>
     /// <param name="builders">A collection of <see cref="ICardBuilder"/> with populated values. An empty instance if method returns <c>false</c>.</param>
     /// <returns><c>true</c> if <paramref name="json"/> was successfully parsed. <c>false</c> if not.</returns>
-    public static bool TryParseMany(string json, out IEnumerable<ICardBuilder> builders)
+    public static bool TryParseMany(string json,
+#if NETSTANDARD2_1 || NET5_0_OR_GREATER
+        [NotNullWhen(true)]
+#endif
+        out IEnumerable<ICardBuilder> builders)
     {
-        builders = Enumerable.Empty<ICardBuilder>();
         try
         {
             IEnumerable<CardBase> models = JsonSerializer.Deserialize<IEnumerable<CardBase>>(json, _options.Value);
@@ -64,10 +76,12 @@ public static bool TryParseMany(string json, out IEnumerable<ICardBuilder> build
                 return true;
             }
 
+            builders = null;
             return false;
         }
         catch
         {
+            builders = null;
             return false;
         }
     }