code: def get_variable(self, variable_name, client=None):
          
          client = self._require_client(client)
          variable = Variable(config=self, name=variable_name)
          try:
              variable.reload(client=client)
              return variable
          except NotFound:
              return None
docs: API call:  get a variable via a ``GET`` request.
  
          This will return None if the variable doesn't exist::
  
            >>> from google.cloud import runtimeconfig
            >>> client = runtimeconfig.Client()
            >>> config = client.config('my-config')
            >>> print(config.get_variable('variable-name'))
            <Variable: my-config, variable-name>
            >>> print(config.get_variable('does-not-exist'))
            None
  
          :type variable_name: str
          :param variable_name: The name of the variable to retrieve.
  
          :type client: :class:`~google.cloud.runtimeconfig.client.Client`
          :param client:
              (Optional) The client to use.  If not passed, falls back to the
              ``client`` stored on the current config.
  
          :rtype: :class:`google.cloud.runtimeconfig.variable.Variable` or None
          :returns: The variable object if it exists, otherwise None.