This is not likely a bug but sort-numeric-fields function does not allow
region with blank lines, while sort-lines does.

This was because sort-skip-fields occurs error with blank line. And when I
added condition for sort-skip-fields like below, sort-numeric-fields was
working with blank lines too.

                     (when (not (string-match-p "^\\s-*$" (thing-at-point
'line)))
                       (sort-skip-fields field))

So, I just hope sort-numeric-fields would work for region with blank lines
too.

I tested with GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version
3.18.9) of 2018-05-29


Always appreciate for contribution.
Thanks.