code: private void readObject(ObjectInputStream in)
          throws IOException, ClassNotFoundException {
          in.defaultReadObject();
          if (prefix == null) {
              prefix = XMLConstants.DEFAULT_NS_PREFIX;
          }
      }
docs: /*
  For old versions of QName which didn't have a prefix field,
  <code>ObjectInputStream.defaultReadObject()</code> will initialize
  the prefix to <code>null</code> instead of the empty string. This
  method fixes up the prefix field if it didn't exist in the serialized
  object.