Removed unused Q.clone().

        obj.negate()

        return obj

    def clone(self):

        clone = self.__class__._new_instance(

            children=[], connector=self.connector, negated=self.negated)

        for child in self.children:

            if hasattr(child, 'clone'):

                clone.children.append(child.clone())

            else:

                clone.children.append(child)

        return clone

    def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):

        # We must promote any new joins to left outer joins so that when Q is

        # used as an expression, rows aren't filtered due to joins.