# assume a foreign key contraint unless defined otherwise
$attrs->{is_foreign_key_constraint} = 1
if not exists $attrs->{is_foreign_key_constraint};
+ $attrs->{undef_on_null_fk} = 1
+ if not exists $attrs->{undef_on_null_fk};
# no join condition or just a column name
if (!ref $cond) {