docs: def application_name(self):
          """
          The name of the remote application for this relation, or ``None``.
  
          This is equivalent to::
  
              relation.units[0].unit_name.split('/')[0]
          """
          if self._application_name is None and self.units:
              self._application_name = self.units[0].unit_name.split('/')[0]
          return self._application_name