Found the following files/directories: ''NULL'' when I run devtools::check_rhub

Question

When I'm running devtools:check_rhub I'm receiving the following note:

❯ checking for non-standard things in the check directory ... NOTE Found the following files/directories: ''NULL''

I am unable to find this NULL file/directory anywhere, even with the ls() command in RStudio. I even deleted my local repo and re-cloned it, but this note persists.

Anyone knows if this is a bug/crash? If don't, how can I solve it?

UPDATE: As noted in R-hub issue #560, this could be due to something in R-hub and not on my package. According to R-hub maintainer, this should be ignored.