<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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