docstring.

Author: WaVEV

django_mongodb/query.py

@@ -178,6 +178,13 @@ def join(self, compiler, connection):
             }
         },
     ]
+
+    # To avoid missing data when using the unwind operator,
+    # an empty collection should be added if the join is not an inner join.
+    # For inner joins, rows with empty arrays are removed,
+    # as the unwind operator unrolls or unnests the array and removes the row if it is empty.
+    # This is the expected behavior for inner joins.
+    # However, for left outer joins (LOUTER), an empty collection is returned instead.
     if self.join_type != INNER:
         lookup_pipeline.append(
             {