In Java 11, Class#newInstance is deprecated, as it does not work correctly with Exceptions. The suggested replacement is to use getDeclaredConctructor(). But we decided to use getConstructor(), as all dynamic code who instantiates a class, e.g., from a config file, should only do this using public APIs.
But this caused Solr to fail as some config files refer this class, which is "package private"! So we should fix this bug and make the class public! All managed-schema files are referring a package private class (as default).
In the Java-11 branch we already fixed this, but it's a bug also in Java 8. It just works, because the code who instantiates the class is luckily in the correct package.