<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def confirm_reservation(self, username, domain, password, email=None):
 """Confirm a reservation for a username. The default implementation just calls :py:func:`~xmpp_backends.base.XmppBackendBase.set_password` and optionally :py:func:`~xmpp_backends.base.XmppBackendBase.set_email`. """

        self.set_password(username=username, domain=domain, password=password)
        if email is not None:
            self.set_email(username=username, domain=domain, email=email)