<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def depart(self):
 """ Remove the current remote unit, for the active hook context, from this conversation. This should be called from a `-departed` hook. """

        unit = hookenv.remote_unit()
        self.units.remove(unit)
        if self.units:
            unitdata.kv().set(self.key, self.serialize(self))
        else:
            unitdata.kv().unset(self.key)