Check that XDG base directories paths are absolute
The spec reads:
All paths set in these environment variables must be absolute. If an implementation encounters a relative path in any of these variables it should consider the path invalid and ignore it.
and
If $XDG_DATA_HOME is either not set or empty, a default equal to $HOME/.local/share should be used.
Testing that the path is absolute also entails that is is non-empty.