Steps to Reproduce

1. Run flutter gen-l10n --help.
2. See the help of --[no-]nullable-getter.

Expected results:

"If this value is set to false"

Actual results:

"If this value is set to true"

If this value is set to true,
then a null check is performed on the returned value of
Localizations.of(context), removing the need for null
checking in user code.

Additional context

A PR (#90180) by someone else to fix this has been closed without being merged because of a missing test.

I gave up fixing it myself, not knowing what test was needed, but I thought I should at least file an issue about it so that it'd catch someone's eye.