Checks if NULL or passes test.
Examples
chk_null_or(NULL, chk_number)
#> Warning: The `chk` argument of `chk_null_or()` is deprecated as of chk 0.6.1.
#> ℹ Please use the `vld` argument instead.
chk_null_or(1, chk_number)
try(chk_null_or("1", chk_number))
#> Error in eval(expr, envir) :
#> `"1"` must be a number (non-missing numeric scalar) or NULL.