def _FormatUsername(self, event):
    """Formats the username.

    Args:
      event (EventObject): event.

     Returns:
       str: formatted username field.
    """
    username = self._output_mediator.GetUsername(event)
    return self._SanitizeField(username)
Formats the username.

    Args:
      event (EventObject): event.

     Returns:
       str: formatted username field.