docs: private static void filterClasses(final Collection<Class<?>> classes) {
          final Iterator<Class<?>> iterator = classes.iterator();
          while (iterator.hasNext()) {
              final Class<?> clazz = iterator.next();
              if (clazz.isAnnotation() || !Reflections.isConcrete(clazz)) {
                  iterator.remove();
              }
          }
      }