Update AbstractionMapper.cs

Author: MehmetTarikKirsanli

src/OllamaSharp/MicrosoftAi/AbstractionMapper.cs

@@ -358,8 +358,8 @@ public static ChatResponseUpdate ToChatResponseUpdate(ChatResponseStream? respon
 				ModelId = done.Model
 			};
 		}
-		
-		return new ChatResponseUpdate(ToAbstractionRole(response?.Message.Role), contents)
+
+		return new ChatResponseUpdate(ToAbstractionRole(response?.Message?.Role), contents)
 		{
 			// no need to set "Contents" as we set the text
 			CreatedAt = response?.CreatedAt,
@@ -536,4 +536,4 @@ public static GeneratedEmbeddings<Embedding<float>> ToGeneratedEmbeddings(EmbedR
 			}
 		};
 	}
-}
+}