[Bug] payload assignment in exceptions.py does not handle list type correctly

[AlexChim1231]

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Please run down the following list and make sure you've tried the usual "quick fixes":

• Search the issues already opened: https://github.com/googleapis/python-api-core/issues
• Search StackOverflow: https://stackoverflow.com/questions/tagged/google-cloud-platform+python

If you are still having issues, please be sure to include as much information as possible:

Environment details

• OS type and version: Windows 11

• Python version: python --version 3.11.9

• pip version: pip --version 24.0

• google-api-core version: pip show google-api-core 2.25.1

• Dify version: v1.6.0

• Dify Vertex AI Plugin version: 0.22.0

Steps to reproduce

1. Set up Dify with Vertex AI with unsupport location (e.g. asia-southeast1), not
2. Call Gemini 2.5 Pro in Workflow or Chatflow

Code example

N/A, I can only reproduce this error via Dify. But after I look at the source code, they call gemini though import vertexai.generative_models or from google import genai

Stack trace

Traceback (most recent call last):
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\dify_plugin\core\server\io_server.py", line 92, in _execute_request_in_thread    
    self._execute_request(
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\dify_plugin\plugin.py", line 337, in _execute_request
    for message in response:
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\dify_plugin\interfaces\model\large_language_model.py", line 617, in invoke       
    yield from result
  File "C:\Users\Alex.chim\Documents\GitHub\dify-official-plugins\models\vertex_ai\models\llm\llm.py", line 619, in _handle_generate_stream_response
    for chunk in response:
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\vertexai\generative_models\_generative_models.py", line 861, in _generate_content_streaming
    response_stream = self._prediction_client.stream_generate_content(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\google\cloud\aiplatform_v1\services\prediction_service\client.py", line 2289, in stream_generate_content
    response = rpc(
               ^^^^
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\google\api_core\gapic_v1\method.py", line 131, in __call__
    return wrapped_func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\google\api_core\grpc_helpers.py", line 76, in error_remapped_callable
    return callable_(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\google\cloud\aiplatform_v1\services\prediction_service\transports\rest.py", line 1555, in __call__
    raise core_exceptions.from_http_response(response)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\google\api_core\exceptions.py", line 557, in from_http_response
    return format_http_response_error(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Alex.chim\AppData\Local\Programs\Python\Python311\Lib\site-packages\google\api_core\exceptions.py", line 517, in format_http_response_error
    error_message = payload.get("error", {}).get("message", "unknown error")
                    ^^^^^^^^^^^
AttributeError: 'list' object has no attribute 'get'

Making sure to follow these steps will guarantee the quickest resolution possible.

Thanks!

[AlexChim1231]

Screen Shot about the error