docs: @Override
    public void writeExternal(ObjectOutput out) throws IOException {
      out.writeInt(getPageID());
      out.writeBoolean(isLeaf());
      out.writeBoolean(supernode);
      out.writeInt(numEntries);
      out.writeInt(entries.length);
      if(isSuperNode())
        return; // cannot fit this into out
      for(Entry entry : entries) {
        if(entry == null) {
          break;
        }
        entry.writeExternal(out);
      }
    }