filter out /dev/null entries in list of patch files for PR

Ran into this issue when testing https://github.com/hpcugent/easybuild-easyconfigs/pull/1217, see https://github.com/hpcugent/easybuild-easyconfigs/pull/1217.diff
what is a "patches files"? the patches? the files to be patched? the files that have been patched?