error message on install: "called emacs-package-install as a new-style add-on"

The following error message was emitted while installing scala-mode-el via aptitude:

Setting up scala-mode-el (20111005-2.1) ...
ERROR: scala-mode-el is broken - called emacs-package-install as a new-style add-on, but has no compat file.
Install scala-mode-el for emacs
Install scala-mode-el for emacs

It also appears to be pretty out-of-date wrt upstream.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: scala-mode-el 20111005-2.1
ProcVersionSignature: Ubuntu 5.8.0-48.54-generic 5.8.18
Uname: Linux 5.8.0-48-generic x86_64
ApportVersion: 2.20.11-0ubuntu50.5
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Sun Apr 18 13:00:03 2021
Dependencies:

DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-trusty-amd64-osp1-20150720-0
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-04-15 (1829 days ago)
InstallationMedia: Ubuntu 14.04 "Trusty" - Build amd64 LIVE Binary 20150720-04:06
PackageArchitecture: all
RebootRequiredPkgs:
 linux-image-5.8.0-49-generic
 linux-base
SourcePackage: scala-mode-el
UpgradeStatus: Upgraded to groovy on 2020-12-22 (117 days ago)