The solution is here: https://github.com/brianchandotcom/liferay-portal/pull/15426/files
You have to implement an ext that override liferay-portal / portal-impl / src / com / liferay / portlet / documentlibrary / service / impl / DLAppHelperLocalServiceImpl.java
You start from old class and add only necessaries changes (Not the entire file!)
It's the easiest way.