I came across this issue because there is bug in CAL10N code (filled separately) that is crashing the compiler. But the reason for this issue is different. Slf4j-ext contains different extensions. In my case we are not even using features from cal10n, but because of slf4j-ext it is now scanning and checking my code regardless (from 0.8). Make slf4j-ext usage of CAL10N as optional dependency.
In order to use CAL10N in a project, all you need is to add cal10n-api-0.8.1.jar onto your project's class path.