;   } catch (IOException shouldNeverHappen) {    throw new FlinkRuntimeException(shouldNeverHappen);   }  }   /**   * Returns a serialized composite key, from the key and key-group provided in a previous call to   * {@link #setKeyAndKeyGroup(Object, int)} and the given namespace.   *   * @param namespace           the namespace to concatenate for the serialized composite key bytes.   * @param namespaceSerializer the serializer to obtain the serialized form of the namespace.   * @param <N>                 the type of the namespace.   * @return the bytes for the serialized composite key of key-group, key, namespace.   */  @Nonnull  public <N