code: def test_empty_string_ignored_prefixed(self):
      with patch.dict(
          in_dict=os.environ,
          AIRFLOW_CONN_MY_CONN=json.dumps(
              {
                  "password": "hi",
                  "extra": {
                      "extra__slack__base_url": "",
                      "extra__slack__proxy": "",
                  },
              }
          ),
      ):
          hook = SlackHook(slack_conn_id="my_conn")
          params = hook._get_conn_params()
          assert "proxy" not in params
          assert "base_url" not in params
  
imports: from __future__ import annotations
  import json
  import os
  from typing import Any
  from unittest import mock
  from unittest.mock import patch
  import pytest
  from slack_sdk.errors import SlackApiError
  from slack_sdk.http_retry.builtin_handlers import ConnectionErrorRetryHandler, RateLimitErrorRetryHandler
  from slack_sdk.web.slack_response import SlackResponse
  from airflow.exceptions import AirflowNotFoundException
  from airflow.models.connection import Connection
  from airflow.providers.slack.hooks.slack import SlackHook
label_desc: Use image node_id 15 for calling the TestSlackHook obj's underlying member method code with example usage: obj.test_empty_string_ignored_prefixed() without return types