docstr: Test that if the key with connection ID is not present in SSM,
  SystemsManagerParameterStoreBackend.get_connection should return None
docstr_tok: ["Test","that","if","the","key","with","connection","ID","is","not","present","in","SSM",",","SystemsManagerParameterStoreBackend.get_connection","should","return","None"]
code: def test_get_conn_value_non_existent_key(self):
      """
      Test that if the key with connection ID is not present in SSM,
      SystemsManagerParameterStoreBackend.get_connection should return None
      """
      conn_id = "test_mysql"
      param = {
          "Name": "/airflow/connections/test_postgres",
          "Type": "String",
          "Value": "postgresql://airflow:airflow@host:5432/airflow",
      }
  
      ssm_backend = SystemsManagerParameterStoreBackend()
      ssm_backend.client.put_parameter(**param)
  
      assert ssm_backend.get_conn_value(conn_id=conn_id) is None
      assert ssm_backend.get_connection(conn_id=conn_id) is None
  
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 3 for calling the TestSsmSecrets obj's underlying member method code with example usage: obj.test_get_conn_value_non_existent_key() without return types