def METHOD_NAME(self, obj):
    if not obj._signal:
        return None
    serialized_location = LocationModelSerializer(obj._signal_location).data
    serialized_location = serialized_location or None  # We want null in stead of {}
    return {
        'signal_id': obj._signal.uuid,
        'id': obj._signal.id,
        'location': serialized_location
    }