ubiquity hook 'str' object has no attribute 'decode', again

[eaglgenes101]

This bug is almost entirely a description-by-description copy of this bug: https://bugs.launchpad.net/ubuntu/+source/apport/+bug/1501773

Only differences are that the version I'm trying to install is artful, not wily, and the first line reported is 198, not 197.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: ubiquity 17.10.10
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CasperVersion: 1.387
Date: Wed Dec 27 11:55:10 2017
LiveMediaBuild: Ubuntu 17.10 "Artful Aardvark" - Release amd64 (20171018)
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.