https://github.com/Rdatatable/data.table/blob/26bb18e163a2de29cf75ed430175bd9abf12e7ad/inst/tests/tests.Rraw#L9446

We are un-exporting S3 methods in {bit64}, which will break this test. Plain is.na should suffice.

This change to {bit64} will not be put on CRAN until at least 2027 so I don't expect this to require a patch.