pm/sleep.d/55NetworkManager calls the
org.freedesktop.NetworkManager.sleep and
org.freedesktop.NetworkManager.wake methods. However, since
NetworkManager version 7 they don't exist any more, and have been
replaced by org.freedesktop.NetworkManager.Sleep which takes a boolean
argument indicating whether NetworkManager should sleep (true) or not
(false).

I already reported this issue to upstream:
https://bugs.freedesktop.org/show_bug.cgi?id=42500

Cheers

Michael

Attached patch fixes the issue for me.

The patch looks good.

I came up with the same solution, and have reported it in Launchpad at:
https://launchpad.net/bugs/1007924

Dear submitter,

as the package pm-utils has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/1058701

The version of this package that was in Debian prior to this removal
can still be found using https://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Thorsten Alteholz (the ftpmaster behind the curtain)