diff --git a/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentSession.cs b/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentSession.cs
index 400bfbcaf6..102aee83e6 100644
--- a/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentSession.cs
+++ b/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgentSession.cs
@@ -21,8 +21,13 @@ internal ChatClientAgentSession()
     {
     }
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ChatClientAgentSession"/> class with optional conversation and state data.
+    /// </summary>
+    /// <param name="conversationId">The underlying service chat history identifier, if available.</param>
+    /// <param name="stateBag">The state bag to initialize the session with.</param>
     [JsonConstructor]
-    internal ChatClientAgentSession(string? conversationId, AgentSessionStateBag? stateBag) : base(stateBag ?? new())
+    internal ChatClientAgentSession(string? conversationId = null, AgentSessionStateBag? stateBag = null) : base(stateBag ?? new())
     {
         this.ConversationId = conversationId;
     }
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentSessionTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentSessionTests.cs
index 1f5e5aa9cd..20bf40c393 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentSessionTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentSessionTests.cs
@@ -3,6 +3,7 @@
 using System;
 using System.Linq;
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using Microsoft.Extensions.AI;
 
 #pragma warning disable CA1861 // Avoid constant arrays as arguments
@@ -117,6 +118,27 @@ public void DeserializeWithInvalidJsonThrows()
         Assert.Throws<ArgumentException>(() => ChatClientAgentSession.Deserialize(invalidJson));
     }
 
+    [Fact]
+    public void VerifyDeserializeWithWhenWritingNullOptions()
+    {
+        // Arrange
+        var session = new ChatClientAgentSession();
+        JsonSerializerOptions options = new()
+        {
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+            RespectRequiredConstructorParameters = true,
+        };
+        options.TypeInfoResolverChain.Add(AgentJsonUtilities.DefaultOptions.TypeInfoResolver!);
+
+        // Act
+        var serializedSession = JsonSerializer.SerializeToElement(session, options.GetTypeInfo(typeof(ChatClientAgentSession)));
+        var deserializedSession = ChatClientAgentSession.Deserialize(serializedSession, options);
+
+        // Assert
+        Assert.False(serializedSession.TryGetProperty("conversationId", out _));
+        Assert.Null(deserializedSession.ConversationId);
+    }
+
     #endregion Deserialize Tests
 
     #region Serialize Tests