code: @SuppressWarnings("unchecked")
      protected Collection _transform(final Collection collection) {
          if (collection == null) return null;
          if (collection instanceof BeanCollection) return collection;
          return new BeanCollection(collection, this);
      }
docs: <p>_transform.</p>
  
  @param collection a {@link java.util.Collection} object.
  @return a {@link java.util.Collection} object.