Fix handling unset response_schema being passed to gemini models

Use of `is_none_or_empty' doesn't work well with classes, which
response_schema can get set to.

src/khoj/processor/conversation/google/gemini_chat.py

@@ -140,8 +140,8 @@ def gemini_send_message_to_model(
     """
     model_kwargs = {}
 
-    # This caused unwanted behavior and terminates response early for gemini 1.5 series. Monitor for flakiness with 2.0 series.
-    if response_type == "json_object" and model in ["gemini-2.0-flash"]:
+    # Monitor for flakiness in 1.5+ models. This would cause unwanted behavior and terminate response early in 1.5 models.
+    if response_type == "json_object" and not model.startswith("gemini-1.5"):
         model_kwargs["response_mime_type"] = "application/json"
         if response_schema:
             model_kwargs["response_schema"] = response_schema

src/khoj/processor/conversation/google/utils.py

@@ -89,7 +89,7 @@ def gemini_completion_with_backoff(
 
     # format model response schema
     response_schema = None
-    if model_kwargs and not is_none_or_empty(model_kwargs.get("response_schema")):
+    if model_kwargs and model_kwargs.get("response_schema"):
         response_schema = clean_response_schema(model_kwargs["response_schema"])
 
     seed = int(os.getenv("KHOJ_LLM_SEED")) if os.getenv("KHOJ_LLM_SEED") else None