Additionally as blackboxsw pointed out to me recently the man page says it will default to the previous value, which actually makes sense.
| --release, -r
| Finalize the changelog for a release. Update the changelog
| timestamp. If the distribution is set to UNRELEASED, change it
| to the distribution from the previous changelog entry (or
| another distribution as specified by --distribution). If there
| are no previous changelog entries and an explicit distribution
| has not been specified, unstable will be used.
Additionally as blackboxsw pointed out to me recently the man page says it will default to the previous value, which actually makes sense.
| --release, -r
| Finalize the changelog for a release. Update the changelog
| timestamp. If the distribution is set to UNRELEASED, change it
| to the distribution from the previous changelog entry (or
| another distribution as specified by --distribution). If there
| are no previous changelog entries and an explicit distribution
| has not been specified, unstable will be used.