<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _FormatTag(self, event):
 """Formats the event tag. Args: event (EventObject):
 event. Returns: str: event tag field. """

    tag = getattr(event, 'tag', None)

    if not tag:
      return '-'

    return ' '.join(tag.labels)