eZDir::path() does not accept a '/' as a path by default, it will return an empty string in this case. Only if $includeEndSeparator is true will it keep the slash. The patch fixes this by not removing the end separator when it is the only character in the path.
NB: This issue should not be patched until the following issue is also patched:
#015823: Running cache clearing procedure from upgrade 4.2.0 using root removes all linux system files