Not immediately clear what's wronng in "manual partitioning" dialog when mount point is not set

The manual partitioning dialog permits allocating an ext4 partition without a mount point.
As a result, the "Next" button is greyed out and it is not immediately clear what's wrong.

Also: after setting a mount point, it is impossible to unset it.

ProblemType: Bug
DistroRelease: Ubuntu 23.10
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 6.3.0-7.7-generic 6.3.5
Uname: Linux 6.3.0-7-generic x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.27.0-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.482
CurrentDesktop: ubuntu:GNOME
Date: Sat Aug 26 05:13:47 2023
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz layerfs-path=standard.live.squashfs --- quiet splash
LiveMediaBuild: Ubuntu 23.10 "Mantic Minotaur" - Daily amd64 (20230825)
ProcEnviron:
 LANG=C.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 XDG_RUNTIME_DIR=<set>
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)