Fix none() no-match condition for aggregation + update changelog

Author: bagerard

docs/changelog.rst

@@ -12,6 +12,7 @@ Development
 - BREAKING CHANGE: connecting MongoEngine with mongomock should now use the new `mongo_client_class`
   For more info, check https://docs.mongoengine.org/guide/mongomock.html
 - Fix DictField that always gets marked as changed #2606
+- fix for Queryset.none() that has no effect on update/aggregate / first #2669
 
 Changes in 0.26.0
 =================

mongoengine/queryset/base.py

@@ -1316,7 +1316,7 @@ def aggregate(self, pipeline, *suppl_pipeline, **kwargs):
         initial_pipeline = []
         if self._none or self._empty:
             initial_pipeline.append({"$limit": 1})
-            initial_pipeline.append({"$match": {"fldksjhkjhafds": "lasdjfhlasdhfk"}})
+            initial_pipeline.append({"$match": {"$expr": False}})
 
         if self._query:
             initial_pipeline.append({"$match": self._query})