@SuppressWarnings("unchecked") private <T extends Element>List<T> castElementList(Object obj){
  return (List<T>)obj;
}

@ SuppressWarnings ( "unchecked" ) private < T extends Element > List < T > castElementList ( Object obj ) { return ( List < T > ) obj ; }
suppress the warnings around casting the object in the map into a list of elements .
