fix isnull lookup

.github/workflows/test-python.yml

@@ -71,6 +71,8 @@ jobs:
           defer_regress
           from_db_value
           lookup.tests.LookupTests.test_escaping
+          lookup.tests.LookupTests.test_isnull_textfield
+          lookup.tests.LookupQueryingTests.test_isnull_lookup_in_filter
           model_fields
           or_lookups
           sessions_tests

django_mongodb/query.py

@@ -273,16 +273,6 @@ def _decode_child(self, child):
 
         lookup_type = child.lookup_name
 
-        # Since NoSql databases generally don't support aggregation or
-        # annotation, pass true unless the query has a get_aggregation() method.
-        # It's a little troubling however that the _nomalize_lookup_value
-        # method seems to only use this value in the case that the value is an
-        # iterable and the lookup_type equals isnull.
-        annotation = (
-            self.get_aggregation(using=self.connection)[None]
-            if hasattr(self, "get_aggregation")
-            else True
-        )
         value = rhs_params
         packed = child.lhs.get_group_by_cols()[0]
         alias = packed.alias
@@ -303,11 +293,11 @@ def _decode_child(self, child):
 
             field = next(f for f in opts.fields if f.column == column)
 
-        value = self._normalize_lookup_value(lookup_type, value, field, annotation)
+        value = self._normalize_lookup_value(lookup_type, value, field)
 
         return field, lookup_type, value
 
-    def _normalize_lookup_value(self, lookup_type, value, field, annotation):
+    def _normalize_lookup_value(self, lookup_type, value, field):
         """
         Undo preparations done by lookups not suitable for MongoDB, and pass
         the lookup argument through DatabaseOperations.prep_lookup_value().
@@ -320,7 +310,7 @@ def _normalize_lookup_value(self, lookup_type, value, field, annotation):
                     "not to be a list. Only 'in'-filters can be used with "
                     "lists." % lookup_type
                 )
-            value = annotation if lookup_type == "isnull" else value[0]
+            value = value[0]
 
         # Remove percent signs added by PatternLookup.process_rhs() for LIKE
         # queries.