:meth:`.Query.merge_result` can now load rows from an outer join

where an entity may be ``None`` without throwing an error.
[ticket:2640]

1 files changed, 5 insertions, 4 deletions

diff --git a/lib/sqlalchemy/orm/loading.py b/lib/sqlalchemy/orm/loading.py
index baff076eb..5937197fd 100644
--- a/lib/sqlalchemy/orm/loading.py
+++ b/lib/sqlalchemy/orm/loading.py
@@ -129,10 +129,11 @@ def merge_result(query, iterator, load=True):
             for row in iterator:
                 newrow = list(row)
                 for i in mapped_entities:
-                    newrow[i] = session._merge(
-                            attributes.instance_state(newrow[i]),
-                            attributes.instance_dict(newrow[i]),
-                            load=load, _recursive={})
+                    if newrow[i] is not None:
+                        newrow[i] = session._merge(
+                                attributes.instance_state(newrow[i]),
+                                attributes.instance_dict(newrow[i]),
+                                load=load, _recursive={})
                 result.append(util.KeyedTuple(newrow, keys))
 
         return iter(result)