Database Users

I want to get the category id from parentCategories property  of a product in java , then iterate them until a specific category comes up. But , I am getting class cast exception on line number 2 . Please help me. java.lang.ClassCastException: atg.adapter.gsa.ChangeAwareSet cannot be cast to java.util.List 1) RepositoryItem productItem = getCatalogTools().findProduct(id);2) List<RepositoryItem> catList = (List<RepositoryItem>)productItem.getPropertyValue("parentCategories"); 3)  for (RepositoryItem category : catList) {  vlogDebug("Category:{0}", category.getRepositoryId());}