diff --git a/backend/open_webui/utils/schemas.py b/backend/open_webui/utils/schemas.py
index 958e57318..4d1d448cd 100644
--- a/backend/open_webui/utils/schemas.py
+++ b/backend/open_webui/utils/schemas.py
@@ -104,5 +104,9 @@ def json_schema_to_pydantic_type(json_schema: dict[str, Any]) -> Any:
         return Optional[Any]  # Use Optional[Any] for nullable fields
     elif type_ == "literal":
         return Literal[literal_eval(json_schema.get("enum"))]
+    elif type_ == "optional":
+        inner_schema = json_schema.get("items", {"type": "string"})
+        inner_type = json_schema_to_pydantic_type(inner_schema)
+        return Optional[inner_type]
     else:
         raise ValueError(f"Unsupported JSON schema type: {type_}")