queryset transform tries to update query dictionary with regex pattern

[aeroeng]

ResultRecord.objects(Q( defects__number__iexact='FFF-10219') & Q(defects__number__exists=True))
Traceback (most recent call last):
File "", line 1, in
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/queryset.py", line 58, in repr
self._populate_cache()
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/queryset.py", line 93, in _populate_cache
self._result_cache.append(self.next())
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py", line 1137, in next
raw_doc = self._cursor.next()
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py", line 1182, in _cursor
self._cursor_obj = self._collection.find(self._query,
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py", line 1215, in _query
self._mongo_query = self._query_obj.to_query(self._document)
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 92, in to_query
query = query.accept(QueryCompilerVisitor(document))
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 157, in accept
return visitor.visit_query(self)
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 80, in visit_query
return transform.query(self.document, **query.query)
File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/transform.py", line 116, in query
mongo_query[key].update(value)
TypeError: '_sre.SRE_Pattern' object is not iterable

[DavidBord]

@aeroeng, could you please provide a test that reproduces this error?