Gentoo's Bugzilla –
Attachment 440724 Details for
Bug 588840sys-auth/consolekit-1.1.0's XDG_RUNTIME_DIR restriction to UID 0 causes ck-launch-session to crash, and pam_ck_connector.so to set value of XDG_RUNTIME_DIR to "(null)"; causing multiple directories having the name of "(null)" to be created