int length = in.readInt();
byte[] buf = new byte[length];
in.readFully(buf);
if (parser == null) {
// create it lazily, static so won't increase object size
parser = new JsonParser();
}
JsonElement o = parser.parse(new String(buf, UTF8));
Field f = getClass().getDeclaredField("intMap");
f.setAccessible(true);
f.set(this, new SimpleIntKeyMap<>());