local-premount/resume script broken, resume fails

On bionic, the initramfs pre-mount/resume script contains this call to /bin/resume:

   /bin/resume ${DEV}

Unfortunately, the ${DEV} variable is never set, causing all resumes to fail, with this error in initramfs.debug:

  + /scripts/local-premount/resume
  + PREREQ=
  + [ -z UUID=16195e13-9fb3-41b2-9671-fb4e1df1ff93 ]
  + [ ! -e /sys/power/resume ]
  + . /scripts/functions
  + . /scripts/local
  + wait-for-root UUID=16195e13-9fb3-41b2-9671-fb4e1df1ff93 5
  + SWAPTYPE=swsuspend
  + [ -x /bin/plymouth ]
  + plymouth --ping
  + [ -n ]
  + /bin/resume
  Usage: /bin/resume /dev/<resumedevice> [offset]

This seems a porting bug: the Debian version (https://anonscm.debian.org/cgit/kernel/initramfs-tools.git/tree/scripts/local-premount/resume) calls local_device_setup(), whioch sets DEV. This call is missing in the Ubuntu (bionic, 0.130ubuntu2) version.

In my case, a simple

   DEV=$(resolve_device "${resume}")

also solved the issue, but I guess the Debian solution is nicer.