See also MC-256823; this is about the toast only, while that's about the ability to have 0-character long titles to begin with while it isn't an optional field.

When an advancement has a 0-character long title (via translation string, or via empty text object), the toast will act as if it is a very long title, and show it via 2 "pages", where the first page is "Advancement get", and the second page is straight up empty.

Steps to reproduce:
Follow the steps from MC-256823, but keep your eye on the toast in the top right of the screen.

Expected behavior:
The toast treats it as a short advancement title and only has one page with "Advancement get" and the title (which is empty)

Current behavior:
The toast treats it as a long advancement title, showing "Advancement get", and then fading it out to make room for the "long" title, resulting in an empty toast.