Alex,
this would happen if ~/.xsession-errors is not a regular file, i. e. symlink to a nonexisting file, or a pipe or something. So in your case /dev/null is not S_ISREG, so it would fall back to creating a new file.
Alex,
this would happen if ~/.xsession-errors is not a regular file, i. e. symlink to a nonexisting file, or a pipe or something. So in your case /dev/null is not S_ISREG, so it would fall back to creating a new file.