docs: public HashMap<Integer, byte[]> preKeyPublicKeysForBundle(TreeMap<Integer, T_PreKey> preKeyHashMap) {
          HashMap<Integer, byte[]> out = new HashMap<>();
          for (Map.Entry<Integer, T_PreKey> e : preKeyHashMap.entrySet()) {
              out.put(e.getKey(), preKeyForBundle(e.getValue()));
          }
          return out;
      }