code: public static <E1,E2> Collection<E2> mapColl2(Iterable<E1> coll, Function<E1,E2> func, Collection<E2> newColl) {
  	for(E1 elem : coll) {
  	    E2 img = func.f(elem);
  	    if(img != null)
  		newColl.add(img);
  	}
  	return newColl;
      }
docs: Similar to <code>mapColl</code>, but filters out all
  <code>null</code> elements produced by <code>func</code>.
  
  @see #mapColl(Iterable, Function, Collection)