docs: @Override
    public void createSafeSpace(SafeSpaceIdentifier safeSpaceId) throws CachePersistenceException {
      if (safeSpaceId == null || !(safeSpaceId instanceof DefaultSafeSpaceIdentifier)) {
        // this cannot happen..if identifier created before creating physical space..
        throw new AssertionError("Invalid safe space identifier. Identifier not created");
      }
      SafeSpace ss = ((DefaultSafeSpaceIdentifier) safeSpaceId).safeSpace;
      FileUtils.create(ss.directory.getParentFile());
      FileUtils.create(ss.directory);
    }