fix: Add type checking to handle different response type of genai API client

Fixes https://github.com/google/adk-python/issues/1514

PiperOrigin-RevId: 773838035

src/google/adk/sessions/vertex_ai_session_service.py

@@ -14,6 +14,7 @@
 from __future__ import annotations
 
 import asyncio
+import json
 import logging
 import re
 from typing import Any
@@ -87,6 +88,7 @@ class VertexAiSessionService(BaseSessionService):
         path=f'reasoningEngines/{reasoning_engine_id}/sessions',
         request_dict=session_json_dict,
     )
+    api_response = _convert_api_response(api_response)
     logger.info(f'Create Session response {api_response}')
 
     session_id = api_response['name'].split('/')[-3]
@@ -100,6 +102,7 @@ class VertexAiSessionService(BaseSessionService):
           path=f'operations/{operation_id}',
           request_dict={},
       )
+      lro_response = _convert_api_response(lro_response)
 
       if lro_response.get('done', None):
         break
@@ -118,6 +121,7 @@ class VertexAiSessionService(BaseSessionService):
         path=f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}',
         request_dict={},
     )
+    get_session_api_response = _convert_api_response(get_session_api_response)
 
     update_timestamp = isoparse(
         get_session_api_response['updateTime']
@@ -149,6 +153,7 @@ class VertexAiSessionService(BaseSessionService):
         path=f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}',
         request_dict={},
     )
+    get_session_api_response = _convert_api_response(get_session_api_response)
 
     session_id = get_session_api_response['name'].split('/')[-1]
     update_timestamp = isoparse(
@@ -167,9 +172,12 @@ class VertexAiSessionService(BaseSessionService):
         path=f'reasoningEngines/{reasoning_engine_id}/sessions/{session_id}/events',
         request_dict={},
     )
+    list_events_api_response = _convert_api_response(list_events_api_response)
 
     # Handles empty response case
-    if list_events_api_response.get('httpHeaders', None):
+    if not list_events_api_response or list_events_api_response.get(
+        'httpHeaders', None
+    ):
       return session
 
     session.events += [
@@ -226,9 +234,10 @@ class VertexAiSessionService(BaseSessionService):
         path=path,
         request_dict={},
     )
+    api_response = _convert_api_response(api_response)
 
     # Handles empty response case
-    if api_response.get('httpHeaders', None):
+    if not api_response or api_response.get('httpHeaders', None):
       return ListSessionsResponse()
 
     sessions = []
@@ -303,6 +312,13 @@ class VertexAiSessionService(BaseSessionService):
     return client._api_client
 
 
+def _convert_api_response(api_response):
+  """Converts the API response to a JSON object based on the type."""
+  if hasattr(api_response, 'body'):
+    return json.loads(api_response.body)
+  return api_response
+
+
 def _convert_event_to_json(event: Event) -> Dict[str, Any]:
   metadata_json = {
       'partial': event.partial,