addressing comments - tidy ups

src/google/adk/tools/google_api_tool/google_api_tool.py

@@ -47,7 +47,7 @@ class GoogleApiTool(BaseTool):
         is_long_running=rest_api_tool.is_long_running,
     )
     self._rest_api_tool = rest_api_tool
-    self._rest_api_tool.set_default_headers(additional_headers or {})
+    if additional_headers: self._rest_api_tool.set_default_headers(additional_headers)
     if service_account is not None:
       self.configure_sa_auth(service_account)
     elif client_id is not None and client_secret is not None:

src/google/adk/tools/google_api_tool/google_api_toolset.py

@@ -67,7 +67,7 @@ class GoogleApiToolset(BaseToolset):
     self._client_id = client_id
     self._client_secret = client_secret
     self._service_account = service_account
-    self._additional_headers = dict(additional_headers or {})
+    self._additional_headers = additional_headers
     self._openapi_toolset = self._load_toolset_with_oidc_auth()
 
   @override

src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py

@@ -128,13 +128,13 @@ class RestApiTool(BaseTool):
         else operation
     )
     self.auth_credential, self.auth_scheme = None, None
-    self._default_headers: Dict[str, str] = {}
 
     self.configure_auth_credential(auth_credential)
     self.configure_auth_scheme(auth_scheme)
 
     # Private properties
     self.credential_exchanger = AutoAuthCredentialExchanger()
+    self._default_headers: Dict[str, str] = {}
     if should_parse_operation:
       self._operation_parser = OperationParser(self.operation)
 
@@ -219,7 +219,7 @@ class RestApiTool(BaseTool):
 
   def set_default_headers(self, headers: Dict[str, str]):
     """Sets default headers that are merged into every request."""
-    self._default_headers = dict(headers)
+    self._default_headers = headers
 
   def _prepare_auth_request_params(
       self,