code: protected final void scan(Package tree) {
      Set<Class<?>> classes = Classes.matching(annotatedWith(Entity.class)).in(tree);
      for (Class<?> clazz : classes) {
        addPersistent(clazz);
      }
    }
docs: Scans all classes in the given package and its subpackages to discover
  classes marked with <code>{@literal @}Entity</code>, which are then mapped
  into this PersistenceModule for storage in the underlying datastore.
  <p>
  This is the equivalent of calling {@link #addPersistent(Class)} for each
  mapped class in the given package tree.
  <p>
  Note that classes not explicitly marked with the <code>{@literal @}Entity</code>
  will be ignored.