docs: public static <E> Set<E> intersection(Set<E> first, Set<E> second) {
          if (first == null || second == null) {
              return EMPTY_SET;
          }
  
          Set<E> intersection = new HashSet<>();
  
          for (E e : first) {
              if (second.contains(e)) {
                  intersection.add(e);
              }
          }
          return intersection;
      }