diff --git a/src/app/endpoints/query.py b/src/app/endpoints/query.py
index 709998ae..e91b8afd 100644
--- a/src/app/endpoints/query.py
+++ b/src/app/endpoints/query.py
@@ -439,8 +439,8 @@ async def query_endpoint_handler_base(  # pylint: disable=R0914
         response = QueryResponse(
             conversation_id=conversation_id,
             response=summary.llm_response,
-            tool_calls=summary.tool_calls if summary.tool_calls else None,
-            tool_results=summary.tool_results if summary.tool_results else None,
+            tool_calls=summary.tool_calls,
+            tool_results=summary.tool_results,
             referenced_documents=referenced_documents,
             truncated=False,  # TODO: implement truncation detection
             input_tokens=token_usage.input_tokens,
diff --git a/src/app/endpoints/query_v2.py b/src/app/endpoints/query_v2.py
index ec14c2c4..1ce31ac6 100644
--- a/src/app/endpoints/query_v2.py
+++ b/src/app/endpoints/query_v2.py
@@ -93,7 +93,6 @@ def _build_tool_call_summary(  # pylint: disable=too-many-return-statements,too-
     Args:
         output_item: An OpenAIResponseOutput item from the response.output array
         rag_chunks: List to append extracted RAG chunks to (from file_search_call items)
-
     Returns:
         A tuple of (ToolCallSummary, ToolResultSummary) one of them possibly None
         if current llama stack Responses API does not provide the information.
diff --git a/src/models/responses.py b/src/models/responses.py
index 44036234..9b005131 100644
--- a/src/models/responses.py
+++ b/src/models/responses.py
@@ -408,13 +408,13 @@ class QueryResponse(AbstractSuccessfulResponse):
         examples=[{"daily": 1000, "monthly": 50000}],
     )
 
-    tool_calls: Optional[list[ToolCallSummary]] = Field(
-        None,
+    tool_calls: list[ToolCallSummary] = Field(
+        default_factory=list,
         description="List of tool calls made during response generation",
     )
 
-    tool_results: Optional[list[ToolResultSummary]] = Field(
-        None,
+    tool_results: list[ToolResultSummary] = Field(
+        default_factory=list,
         description="List of tool results",
     )
 
diff --git a/tests/unit/models/responses/test_successful_responses.py b/tests/unit/models/responses/test_successful_responses.py
index 880b8c49..7e4a6366 100644
--- a/tests/unit/models/responses/test_successful_responses.py
+++ b/tests/unit/models/responses/test_successful_responses.py
@@ -268,8 +268,8 @@ def test_constructor_minimal(self) -> None:
         assert isinstance(response_obj, AbstractSuccessfulResponse)
         assert response_obj.response == "Test response"
         assert response_obj.conversation_id is None
-        assert response_obj.tool_calls is None
-        assert response_obj.tool_results is None
+        assert response_obj.tool_calls == []
+        assert response_obj.tool_results == []
         assert response_obj.referenced_documents == []
         assert response_obj.truncated is False
         assert response_obj.input_tokens == 0