Cast default dict as dict.

Author: WaVEV

django_mongodb/compiler.py

@@ -193,7 +193,7 @@ def _build_aggregation_pipeline(self, ids, group):
                     projected_fields[table][field] = value
                 else:
                     projected_fields[key] = value
-            pipeline.append({"$addFields": projected_fields})
+            pipeline.append({"$addFields": dict(projected_fields)})
             if "_id" not in projected_fields:
                 pipeline.append({"$unset": "_id"})
         return pipeline
@@ -448,7 +448,7 @@ def get_project_fields(self, columns=None, ordering=None):
         if fields and ordering:
             # Add order_by() fields.
             fields.update({alias: expr.as_mql(self, self.connection) for alias, expr in ordering})
-        return fields
+        return dict(fields)
 
     def _get_ordering(self):
         """