Single Checkbox can't be default to 0?

!!Open the same thread in Techical Discussion forum and closed this thread.

We have a single checkbox on the content editor. When it is checked, the value 1. When it is unchecked afterwards, the value became “NULL”. We need to have value 0 for this “unchecked” scenario, and tried to set default value for the field to 0, but it didn’t work, and it still saved “NULL” into the database.

We tried some Transform on the field too, but no luck so far.

Any suggestions/clarifications?