error with `Comment belongs_to :touch => true`

[znz]

I use belongs_to with :touch => true in Comment.
And comment.save! failed.

example application: https://github.com/znz/error-example-for-acts_as_commentable_with_threading

Polymorphic Associations without this gem, commentable_id_was is not 0 but nil.

[znz]

I resolved my problem with referenced issue.
Why the generated default is 0 instead of nil?

[petergoldstein]

The migrations have been fixed on master - #78 - so I'm closing this issue.