docstr: Test that if Variable key is not present in SSM,
  SystemsManagerParameterStoreBackend.get_config should return None,
  SystemsManagerParameterStoreBackend._get_secret should not be called
docstr_tok: ["Test","that","if","Variable","key","is","not","present","in","SSM",",","SystemsManagerParameterStoreBackend.get_config","should","return","None",",","SystemsManagerParameterStoreBackend._get_secret","should","not","be","called"]
code: def test_config_prefix_none_value(self, mock_get_secret):
      """
      Test that if Variable key is not present in SSM,
      SystemsManagerParameterStoreBackend.get_config should return None,
      SystemsManagerParameterStoreBackend._get_secret should not be called
      """
      kwargs = {"config_prefix": None}
  
      ssm_backend = SystemsManagerParameterStoreBackend(**kwargs)
  
      assert ssm_backend.get_config("config") is None
      mock_get_secret.assert_not_called()
  
imports: from __future__ import annotations
  import json
  from unittest import mock
  import pytest
  from moto import mock_ssm
  from airflow.configuration import initialize_secrets_backends
  from airflow.providers.amazon.aws.secrets.systems_manager import SystemsManagerParameterStoreBackend
  from tests.test_utils.config import conf_vars
label_desc: Use image node_id 11 for calling the TestSsmSecrets obj's underlying member method code with example usage: obj.test_config_prefix_none_value(mock_get_secret) without return types