Register a system role.

        .. note:: A system role can't be registered two times. If it happens,
        then an assert exception will be raised.

        :param system_role: The system role to be registered.

def register_system_role(self, system_role):
        """Register a system role.

        .. note:: A system role can't be registered two times. If it happens,
        then an assert exception will be raised.

        :param system_role: The system role to be registered.
        """
        assert system_role.value not in self.system_roles
        self.system_roles[system_role.value] = system_role