docs: public ObjectHashSet<T> difference(final ObjectHashSet<T> other)
      {
          ObjectHashSet<T> difference = null;
  
          for (final T value : values)
          {
              if (value != MISSING_VALUE && !other.contains(value))
              {
                  if (difference == null)
                  {
                      difference = new ObjectHashSet<>(size);
                  }
  
                  difference.add(value);
              }
          }
  
          return difference;
      }