Warning: Undefined array key "version" in .../leaflet/leaflet.install on line 45

I'm picking this issue and try to reproduce the problem :)

This is not a big deal, at all.
I just checked this and I cannot reproduce.
With the actual Leaflet 10.2.25 release, and Leaflet js local library, marked as 19.4 all looks being reported as expected in the Status Report page and in the XDebug report.
So I am asking myself what kind of use case are dealing with ...

Anyway, worth adding a fallback string to that code line logics and I just did it in this latest commit:
https://git.drupalcode.org/project/leaflet/-/commit/7ea8a00a229f435d7f94...