docs: @Override
  	public RocksDBRestoreResult restore()
  		throws IOException, StateMigrationException, RocksDBException {
  		openDB();
  		for (KeyedStateHandle keyedStateHandle : restoreStateHandles) {
  			if (keyedStateHandle != null) {
  
  				if (!(keyedStateHandle instanceof KeyGroupsStateHandle)) {
  					throw new IllegalStateException("Unexpected state handle type, " +
  						"expected: " + KeyGroupsStateHandle.class +
  						", but found: " + keyedStateHandle.getClass());
  				}
  				this.currentKeyGroupsStateHandle = (KeyGroupsStateHandle) keyedStateHandle;
  				restoreKeyGroupsInStateHandle();
  			}
  		}
  		return new RocksDBRestoreResult(this.db, defaultColumnFamilyHandle, nativeMetricMonitor,
  			-1, null, null);
  	}