def referenced_by(self, refobj):
        """Return the reference that holds the given reftrack node.

        Returns None if it is imported/in the current scene.

        :param refobj: the reftrack node to query
        :type refobj: str
        :returns: the reference node that holds the given refobj
        :rtype: str | None
        :raises: None
        """
        try:
            ref = cmds.referenceQuery(refobj, referenceNode=True)
            return ref
        except RuntimeError as e:
            if str(e).endswith("' is not from a referenced file.\n"):
                return None
            else:
                raise e