fix: keep type field in Gemini schema when properties is empty (#18979)

litellm/llms/vertex_ai/common_utils.py

@@ -660,11 +660,11 @@ def add_object_type(schema):
         if "required" in schema and schema["required"] is None:
             schema.pop("required", None)
         # Gemini doesn't accept empty properties for object types
-        # If properties is empty, remove it and the type field
+        # If properties is empty, remove it but keep type as object
         if not properties:
             schema.pop("properties", None)
-            schema.pop("type", None)
             schema.pop("required", None)
+            schema["type"] = "object"
         else:
             schema["type"] = "object"
             for name, value in properties.items():

tests/test_litellm/llms/vertex_ai/test_gemini_empty_properties.py

@@ -0,0 +1,16 @@
+"""Test for Gemini schema handling with empty properties."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.abspath("../../../.."))
+
+from litellm.llms.vertex_ai.common_utils import add_object_type
+
+
+def test_add_object_type_empty_properties_keeps_type():
+    """Gemini requires type: object even when properties is empty."""
+    schema = {"properties": {}, "type": "object"}
+    add_object_type(schema)
+    assert schema.get("type") == "object"
+    assert "properties" not in schema

tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py

@@ -1297,8 +1297,8 @@ def test_build_vertex_schema_empty_properties():
     # Verify empty properties was removed
     assert "properties" not in go_back_schema, "Empty properties should be removed"
     
-    # Verify type was also removed (since object without properties is invalid in Gemini)
-    assert "type" not in go_back_schema, "Type should be removed when properties is empty"
+    # Verify type is kept as object (Gemini requires type: object even without properties)
+    assert go_back_schema.get("type") == "object", "Type should be kept as object when properties is empty"
     
     # Verify required was also removed
     assert "required" not in go_back_schema, "Required should be removed when properties is empty"