I have a Dell XPS 13 (9365) and I'm trying to get hibernation working. I had it working on Fedora 28. I could run systemctl hibernate, and the system state would be written to the swap partition and restored at the next boot. After upgrading to Fedora 29, when I try to run systemctl hibernate, it fails and prints an error message
Failed to hibernate system via logind: Resume not configured, can't hibernate
I don't understand this. I never saw this particular message on Fedora 28. Searching the web for it turned up nothing.
My /etc/default/grub includes GRUB_CMDLINE_LINUX="resume=/dev/mapper/fedora-swap..." and that option does show up in /proc/cmdline.
/etc/fstab includes /dev/mapper/fedora-swap swap swap defaults 0 0 and the swap partition is being used. So as far as I can tell, hibernate and resume are configured. Secure boot is disabled in the BIOS.

Does anyone know what this message means and how to fix hibernation?