Set Colormap gives "invalid parameter name 'num colors'"

[Damian Yerrick]

I'm using GIMP 2.10.18-1 on Xubuntu 20.04.1. In Colors > Map > Set Colormap, when I click the Palette: Default button to set the replacement palette, I'm supposed to see a list of palettes from which to choose. Instead, I get the following error:

Plug-in "script-fu"
(/usr/lib/gimp/2.0/plug-ins/script-fu/script-fu)
attempted to install procedure "temp-procedure-number-6" with invalid parameter name "num colors".

These forum references claim that this error is specific to versions 2.10.16 and 2.10.18 and was fixed in 2.10.20:

https://www.reddit.com/r/GIMP/comments/gb5zih/error_when_running_set_colormap_script/
http://gimpchat.com/viewtopic.php?f=9&t=18293

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: gimp 2.10.18-1
ProcVersionSignature: Ubuntu 5.4.0-56.62-generic 5.4.73
Uname: Linux 5.4.0-56-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.13
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Thu Dec 3 19:36:12 2020
InstallationDate: Installed on 2018-06-10 (907 days ago)
InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: gimp
UpgradeStatus: Upgraded to focal on 2020-11-04 (29 days ago)