I had some trouble understanding check_key() when the columns provided is a valid unique key.

If the columns given in the ellipsis ARE a key, the data frame itself is returned silently, so that it can be used for piping.

Small example:

dat <- tibble(a = c(1, 2, 3), b = c(5, 5, 6), c = c(7, 8, 9))
(check_key(dat, a))
NULL

Should dat be returned instead of NULL or should the documentation be modified?