Ticket #1186 (new defect)
mysql _lookup_constraint_references can return None, expected to return iterable.
|Reported by:||stephen@…||Owned by:||andrew|
During column renaming, _lookup_contraint_references is called and the return value is directly assigned to a tuple.  Unfortunately, _lookup_constraint_references sometimes returns None.  I suppose this is probably "never supposed to happen" but I've run into it multiple times when working with renaming columns in m2m through tables.