If you, say, use checkboxes or hidden fields to post the _destroy attribute for nested objects that you allow to be destroyed, 0 or "0" should evaluate as false.

Failing specs:

http://github.com/papercavalier/mongoid/blob/accepts_nested/spec/integration/nested_spec.rb

Fix:

http://github.com/papercavalier/mongoid/commit/6d454e1a9eff0a545e6b3eade7b49ddb1584dfbe