fix QuerySet.annotate() crash with combined expression

Author: timgraham

django_mongodb/compiler.py

@@ -83,7 +83,7 @@ def _make_result(self, entity, columns):
                 if column_alias is not None and column_alias != self.collection_name
                 else entity
             )
-            result.append(obj.get(name, col.field.get_default()))
+            result.append(obj.get(name))
         return result
 
     def check_query(self):

django_mongodb/features.py

@@ -275,11 +275,6 @@ def django_test_expected_failures(self):
             "timezones.tests.NewDatabaseTests.test_query_annotation",
         },
         "QuerySet.annotate() has some limitations.": {
-            # annotate() with combined expressions doesn't work:
-            # 'WhereNode' object has no attribute 'field'
-            "lookup.tests.LookupQueryingTests.test_combined_annotated_lookups_in_filter",
-            "lookup.tests.LookupQueryingTests.test_combined_annotated_lookups_in_filter_false",
-            "lookup.tests.LookupQueryingTests.test_combined_lookups",
             # Invalid $project :: caused by :: Unknown expression $count,
             "annotations.tests.NonAggregateAnnotationTestCase.test_combined_expression_annotation_with_aggregation",
             "annotations.tests.NonAggregateAnnotationTestCase.test_combined_f_expression_annotation_with_aggregation",