The lubuntu-desktop package source

Development
1 
$ apt source lubuntu-desktop
Reading package lists... Done
Picking 'lubuntu-meta' as source package instead of 'lubuntu-desktop'
E: Unable to find a source package for lubuntu-meta

$ apt-cache show lubuntu-meta
N: Unable to locate package lubuntu-meta
N: Unable to locate package lubuntu-meta
E: No packages found

Why is that, and how to get the lubuntu-desktop package’s source pls?

2 
$ grep ^deb-src /etc/apt/sources.list
deb-src http://archive.ubuntu.com/ubuntu/ impish main restricted

I.e., the universe is missing from my sources.list