Fix: Add thought_signatures to VertexGeminiConfig and test

litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py

@@ -1811,6 +1811,7 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
         functions: Optional[ChatCompletionToolCallFunctionChunk] = None
         thinking_blocks: Optional[List[ChatCompletionThinkingBlock]] = None
         reasoning_content: Optional[str] = None
+        thought_signatures: Optional[Any] = None
 
         for idx, candidate in enumerate(_candidates):
             if "content" not in candidate:

tests/test_litellm/llms/vertex_ai/gemini/test_vertex_gemini_unbound_local_error.py

@@ -0,0 +1,38 @@
+import pytest
+from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import VertexGeminiConfig
+from litellm import ModelResponse
+
+def test_process_candidates_unbound_local_error_fix():
+    # Setup
+    candidates = [
+        {
+            "content": {
+                "role": "model"
+                # "parts" is missing intentionally to trigger the issue
+            },
+            "finishReason": "STOP"
+        }
+    ]
+    model_response = ModelResponse()
+    
+    # Execution
+    try:
+        VertexGeminiConfig._process_candidates(
+            _candidates=candidates,
+            model_response=model_response,
+            standard_optional_params={},
+            cumulative_tool_call_index=0
+        )
+    except UnboundLocalError as e:
+        pytest.fail(f"UnboundLocalError raised: {e}")
+    except Exception as e:
+        # Other exceptions might be okay if they are not UnboundLocalError, 
+        # but ideally it should pass without error or raise a specific error if parts are required.
+        # However, the goal is to verify thought_signatures doesn't crash.
+        pass
+
+    # Verify that we didn't crash with UnboundLocalError
+
+if __name__ == "__main__":
+    test_process_candidates_unbound_local_error_fix()
+    print("Test passed!")