code: <S extends Storable> void updated(final MapStorage<S> storage, final S old) {
          addToUndoLog(new Undoable() {
              public void undo() {
                  storage.mapPut(old);
              }
  
              @Override
              public String toString() {
                  return "undo update by put: " + old;
              }
          });
      }
docs: Add to undo log.