fix(gemini realtime): empty toolCall must not terminate the WebSocket

If Gemini sends a toolCall whose functionCalls list is empty (or absent),
the previous `continue` left returned_message empty and the
"Unknown message type" guard fired, killing the WebSocket session.
Return a normal (empty) result instead so the session keeps going.

litellm/llms/gemini/realtime/transformation.py

@@ -1238,12 +1238,24 @@ class GeminiRealtimeConfig(BaseRealtimeConfig):
                 )
                 returned_message.append(transformed_message)
             elif openai_event == ResponsesAPIStreamEvents.FUNCTION_CALL_ARGUMENTS_DONE:
-                # Handle toolCall from Gemini. Skip entirely if there are no
-                # function calls in the payload — emitting an orphaned
-                # response.created/response.done pair with no output items
-                # would confuse OpenAI-compatible clients.
+                # Handle toolCall from Gemini. If the payload has no function
+                # calls, emit nothing — an orphaned response.created/done pair
+                # with no output items would confuse OpenAI-compatible clients.
+                # Return rather than ``continue`` so a toolCall that is the
+                # only key in the message doesn't leave ``returned_message``
+                # empty and trip the "Unknown message type" guard below
+                # (which would terminate the WebSocket session).
                 if not value.get("functionCalls"):
-                    continue
+                    return {
+                        "response": returned_message,
+                        "current_output_item_id": current_output_item_id,
+                        "current_response_id": current_response_id,
+                        "current_delta_chunks": current_delta_chunks,
+                        "current_conversation_id": current_conversation_id,
+                        "current_item_chunks": current_item_chunks,
+                        "current_delta_type": current_delta_type,
+                        "session_configuration_request": session_configuration_request,
+                    }
 
                 if current_conversation_id is None:
                     current_conversation_id = f"conv_{uuid.uuid4()}"

tests/test_litellm/llms/gemini/realtime/test_gemini_realtime_transformation.py

@@ -826,6 +826,34 @@ def test_gemini_tool_call_resets_ids_for_post_tool_model_turn():
     )
 
 
+def test_gemini_empty_tool_call_does_not_crash_websocket():
+    """A toolCall payload with no functionCalls must not raise the
+    'Unknown message type' guard — that would terminate the WebSocket session
+    on what is at worst a benign no-op from Gemini."""
+    config = GeminiRealtimeConfig()
+    logging_obj = MagicMock()
+    logging_obj.litellm_trace_id = "trace_empty_tool_call"
+
+    result = config.transform_realtime_response(
+        json.dumps({"toolCall": {"functionCalls": []}}),
+        "gemini-2.5-flash",
+        logging_obj,
+        realtime_response_transform_input={
+            "session_configuration_request": None,
+            "current_output_item_id": None,
+            "current_response_id": None,
+            "current_conversation_id": None,
+            "current_delta_chunks": [],
+            "current_item_chunks": [],
+            "current_delta_type": None,
+        },
+    )
+
+    assert result["response"] == []
+    assert result["current_response_id"] is None
+    assert result["current_output_item_id"] is None
+
+
 def test_gemini_function_call_output_includes_name():
     """Verify function_call_output includes name field from stored mapping."""
     config = GeminiRealtimeConfig()