Good catch. This can happen if you to promise things in the docs without actually having an automated test for it. It used to work, but doesn't anymore due to this special handling of `NA`. (Good to know that `is.na` fails on `NULL` input...) It was my code, so I'm replying here.

The only modification necessary here should be to change this line to `if (!is.null(.id) && is.na(.id)) {`. Everything else should work "as is". Could you please confirm and push again to this branch?