In xdg-screensaver, there are several calls to grep in if control sequences conditions. In order not to get the output of grep, its standard output is redirected to /dev/null.
grep has a -q option that is precisely done for that purpose; in addition it is a bit faster since it exists on the first match since it has no need to wait to the end of its input.
I suggest that you replace all the “grep >/dev/null” by “grep -q”. In addition, the stderr redirections should be removed since they are useful: if an error occurs, it seems more useful to show it rather than hide it.
This has been the object of a bug report for Debian, which I have put in the URL field of this one. There is a patch attached; it is only a first shot which may not be suitable (it removes stderr redirections but adds a -s option which is not very useful) but I can adapt it.