def _str2bool(string):
  """Converts either 'true' or 'false' (not case-sensitively) into a boolean."""
  if string is None:
    return False
  else:
    string = string.lower()

  if string == 'true':
    return True
  elif string == 'false':
    return False
  else:
    raise ValueError(
        'String should either be `true` or `false`: got {}'.format(string))