private static void raiseExceptionIfEmpty(Set<?> foundClasses, String errorFor)
      throws IllegalStateException {
    if (foundClasses == null || foundClasses.isEmpty()) {
      throw new IllegalStateException(
          "Required " + errorFor + " classes were not loaded. Check logs for errors.");
    }
  }
this is used when getting the instance in a cache server. We are getting the
user-command-package from distribution properties. used by OnlineCommandProcessor.
geode-gfsh/src/main/java/org/apache/geode/management/internal/cli/CommandManager.java