Fix chat completion create response

OpenAI.SDK/Managers/OpenAIChatCompletions.cs

@@ -117,16 +117,22 @@ public void Process(ChatCompletionCreateResponse block)
             // We're going to steal the partial message and squirrel it away for the time being.
             if (!IsFnAssemblyActive && isStreamingFnCall)
             {
-                FnCall = firstChoice.Message.FunctionCall;
-                firstChoice.Message.FunctionCall = null;
-                justStarted = true;
+                if (firstChoice.Message != null)
+                {
+                    FnCall = firstChoice.Message.FunctionCall;
+                    firstChoice.Message.FunctionCall = null;
+                    justStarted = true;
+                }
             }
 
             // As long as we're assembling, keep on appending those args
             // (Skip the first one, because it was already processed in the block above)
             if (IsFnAssemblyActive && !justStarted)
             {
-                FnCall.Arguments += ExtractArgsSoFar();
+                if (FnCall != null)
+                {
+                    FnCall.Arguments += ExtractArgsSoFar();
+                }
             }
 
             // If we were assembling and it just finished, fill this block with the info we've assembled, and we're done.

OpenAI.SDK/ObjectModels/RequestModels/ChatMessage.cs

@@ -18,10 +18,10 @@ public class ChatMessage
     ///     length of 64 characters.
     /// </param>
     /// <param name="functionCall">The name and arguments of a function that should be called, as generated by the model.</param>
-    public ChatMessage(string role, string content, string? name = null, FunctionCall? functionCall = null)
+    public ChatMessage(string? role = null, string? content = null, string? name = null, FunctionCall? functionCall = null)
     {
-        Role = role;
-        Content = content;
+        Role = role ?? string.Empty;
+        Content = content ?? string.Empty;
         Name = name;
         FunctionCall = functionCall;
     }
@@ -30,7 +30,7 @@ public ChatMessage(string role, string content, string? name = null, FunctionCal
     ///     The role of the author of this message. One of system, user, or assistant.
     /// </summary>
     [JsonPropertyName("role")]
-    public string Role { get; set; }
+    public string? Role { get; set; }
 
     /// <summary>
     ///     The contents of the message.

OpenAI.SDK/ObjectModels/ResponseModels/ChatCompletionCreateResponse.cs

@@ -7,9 +7,9 @@ public record ChatCompletionCreateResponse : BaseResponse, IOpenAiModels.IId, IO
 {
     [JsonPropertyName("model")] public string Model { get; set; }
 
-    [JsonPropertyName("choices")] public List<ChatChoiceResponse> Choices { get; set; }
+    [JsonPropertyName("choices")] public List<ChatChoiceResponse>? Choices { get; set; }
 
-    [JsonPropertyName("usage")] public UsageResponse Usage { get; set; }
+    [JsonPropertyName("usage")] public UsageResponse? Usage { get; set; }
 
     [JsonPropertyName("created")] public int CreatedAt { get; set; }
 

OpenAI.SDK/ObjectModels/SharedModels/ChatChoiceResponse.cs

@@ -6,15 +6,15 @@ namespace OpenAI.ObjectModels.SharedModels;
 public record ChatChoiceResponse
 {
     [JsonPropertyName("delta")]
-    public ChatMessage Delta
+    public ChatMessage? Delta
     {
         get => Message;
         set => Message = value;
     }
 
-    [JsonPropertyName("message")] public ChatMessage Message { get; set; }
+    [JsonPropertyName("message")] public ChatMessage? Message { get; set; }
 
     [JsonPropertyName("index")] public int? Index { get; set; }
 
-    [JsonPropertyName("finish_reason")] public string FinishReason { get; set; }
+    [JsonPropertyName("finish_reason")] public string? FinishReason { get; set; }
 }