diff --git a/tests/test_openai_source.py b/tests/test_openai_source.py
index 2b361da7e..428ef1566 100644
--- a/tests/test_openai_source.py
+++ b/tests/test_openai_source.py
@@ -273,6 +273,36 @@ async def test_groq_payload_drops_reasoning_content_from_assistant_history():
         await provider.terminate()
 
 
+@pytest.mark.asyncio
+async def test_openai_payload_handles_none_think_content():
+    """Test that _finally_convert_payload handles think content being None."""
+    provider = _make_provider()
+    try:
+        # Test case where think content might be None
+        payloads = {
+            "messages": [
+                {
+                    "role": "assistant",
+                    "content": [
+                        {"type": "think", "think": None},  # type: ignore
+                        {"type": "text", "text": "final answer"},
+                    ],
+                }
+            ]
+        }
+
+        # Should not raise TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'
+        provider._finally_convert_payload(payloads)
+
+        assistant_message = payloads["messages"][0]
+        assert assistant_message["content"] == [
+            {"type": "text", "text": "final answer"}
+        ]
+    finally:
+        await provider.terminate()
+
+
+
 @pytest.mark.asyncio
 async def test_handle_api_error_content_moderated_without_images_raises():
     provider = _make_provider(