code: def validate_is_not_none(config_val, evar):
      
      if config_val is None:
          raise ValueError(
              "Value for environment variable '{evar_name}' can't "
              "be empty.".format(evar_name=evar.name))
      return config_val
docs: If the value is ``None``, fail validation.
  
      :param str config_val: The env var value.
      :param EnvironmentVariable evar: The EVar object we are validating
          a value for.
      :raises: ValueError if the config value is None.