R macos jobs fails

[jangorecki]

https://rdatatable.gitlab.io/data.table/web/checks/data.table/test-mac-rel/00check.log
https://rdatatable.gitlab.io/data.table/web/checks/data.table/test-mac-old/00check.log

macos jobs seem to fail on the function that is testing proper self-referencing of data.table

is.ok = function(x) {
  stopifnot(is.data.table(x))
  capture.output(print(attr(x, ".internal.selfref", TRUE)))!="<pointer: (nil)>"
}

maybe on a mac nil pointer prints differently?