docs: public void writeSuperNode(ObjectOutput out) throws IOException {
      if(!isSuperNode()) {
        throw new IllegalStateException("Cannot write as non-super node via writeSuperNode()");
      }
      // write header
      writeExternal(out);
      for(Entry entry : entries) {
        if(entry == null) {
          break;
        }
        entry.writeExternal(out);
      }
    }