Warning issued: sun.reflect.Reflection.getCallerClass is not supported

Upon start of okapi-core and other okapi test modules, the following warning is issued:

WARNING: sun.reflect.Reflection.getCallerClass is not supported. This will impact performance.

Desired behavior is to prevent this from happening.

Appears after upgrade to OpenJDK 11 (with log4j2). Seems to affect all RMB based modules too (when they start to use OpenJDK 11).