groovy installer crashes on non-efi capable systems

[Harry Coin]

Attempting to install Groovy using cd image. Normal until bootloader install. The system is not EFI capable (older server, some VMs). Installer advises without EFI the system will crash, etc. Though there is a grub/bios partition, and a btrfs install proceeded normally up till the installer bootloader complaint. After choosing 'continue anyway' and being told I'd have to install a boot loader myself, the installer crashed with what you see in this report.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubiquity 20.10.9
ProcVersionSignature: Ubuntu 5.8.0-18.19-generic 5.8.4
Uname: Linux 5.8.0-18-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu45
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.452
Date: Tue Sep 8 10:47:39 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu-mate.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu-MATE 20.10 "Groovy Gorilla" - Alpha amd64 (20200907)
RebootRequiredPkgs:
 linux-image-5.8.0-18-generic
 linux-base
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)