test(vertex_ai/gemini): add tests for BadRequestError on null and empty image_url

Added new test cases to ensure that a BadRequestError is raised when the image_url key is explicitly set to null or is an empty dictionary. These tests validate the handling of edge cases for the image_url field in the Gemini model.

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

@@ -28,3 +28,25 @@ def test_missing_url_inside_image_url_dict_raises_bad_request_error():
     with pytest.raises(litellm.BadRequestError) as exc_info:
         _gemini_convert_messages_with_history(messages, model="gemini-1.5-pro")
     assert "'url' field is missing inside" in str(exc_info.value)
+
+
+def test_explicit_null_image_url_raises_bad_request_error():
+    """When image_url key is present but explicitly null, a BadRequestError is raised."""
+    messages = cast(
+        List[AllMessageValues],
+        [{"role": "user", "content": [{"type": "image_url", "image_url": None}]}],
+    )
+    with pytest.raises(litellm.BadRequestError) as exc_info:
+        _gemini_convert_messages_with_history(messages, model="gemini-1.5-pro")
+    assert "'image_url' field is missing" in str(exc_info.value)
+
+
+def test_empty_dict_image_url_raises_bad_request_error():
+    """When image_url is an empty dict (no url), a BadRequestError is raised."""
+    messages = cast(
+        List[AllMessageValues],
+        [{"role": "user", "content": [{"type": "image_url", "image_url": {}}]}],
+    )
+    with pytest.raises(litellm.BadRequestError) as exc_info:
+        _gemini_convert_messages_with_history(messages, model="gemini-1.5-pro")
+    assert "'url' field is missing inside" in str(exc_info.value)