[bugfix] Fix bug with exploding agent runs due to broken conversion of content Parts to LiteLLM messages format

src/google/adk/models/lite_llm.py

@@ -470,6 +470,8 @@ def _part_has_payload(part: types.Part) -> bool:
     return True
   if part.file_data and (part.file_data.file_uri or part.file_data.data):
     return True
+  if part.function_response:
+    return True
   return False
 
 

tests/unittests/models/test_litellm.py

@@ -1035,6 +1035,23 @@ async def test_generate_content_async_adds_fallback_user_message(
         4,
         id="user content is not the last message scenario",
     ),
+    pytest.param(
+        LlmRequest(
+            contents=[
+                types.Content(
+                    role="user",
+                    parts=[
+                        types.Part.from_function_response(
+                            name="test_function",
+                            response={"result": "test_result"},
+                        )
+                    ],
+                ),
+            ]
+        ),
+        1,
+        id="user content with function_response has payload",
+    ),
 ]