docs: def _check_env_var(envvar: str) -> bool:
      """Check Environment Variable to verify that it is set and not empty.
  
      :param envvar: Environment Variable to Check.
  
      :returns: True if Environment Variable is set and not empty.
  
      :raises: KeyError if Environment Variable is not set or is empty.
  
      .. versionadded:: 0.0.12
      """
      if os.getenv(envvar) is None:
          raise KeyError(
              "Required ENVVAR: {0} is not set".format(envvar))
      if not os.getenv(envvar):  # test if env var is empty
          raise KeyError(
              "Required ENVVAR: {0} is empty".format(envvar))
      return True