Feature summary:

Introduce {{#ifempty: }} parser function, a built-in equivalent for enwiki's {{if empty}} template.
From https://en.wikipedia.org/wiki/Template:If_empty/doc:

It takes any number of parameters and returns the first found to be defined and non-empty. If none is found, nothing is returned. By writing {{if empty|a|b|c}} instead of {{#if:a|a|{{#if:b|b|c}}}}, expression a and b do not have to be repeated and evaluated twice. The template provides a fallback order, similar to a try catch based "It is easier to ask for forgiveness than permission" (EAFP) programming style.

Use case(s):

Replace "If empty" templates and modules across wikis with a built-in parser function (following a recent trend of T359761 and T366623).

Benefits:

All wikis have access to this functionality without the need for creating their own implementation (or copying the template/module).