Parses argument as whitespace-separated list of strings.

    It also parses argument as comma-separated list of strings if requested.

    Args:
      argument: string argument passed in the commandline.

    Returns:
      [str], the parsed flag value.

def parse(self, argument):
    """Parses argument as whitespace-separated list of strings.

    It also parses argument as comma-separated list of strings if requested.

    Args:
      argument: string argument passed in the commandline.

    Returns:
      [str], the parsed flag value.
    """
    if isinstance(argument, list):
      return argument
    elif not argument:
      return []
    else:
      if self._comma_compat:
        argument = argument.replace(',', ' ')
      return argument.split()