def merge!(*args)
      val = args.pop
      keys = args.flatten
      StorageFile.merge!(path, [*@parents, *keys], val)
    end
def merge!(*args)
      val = args.pop
      keys = args.flatten
      StorageFile.merge!(path, [*@parents, *keys], val)
    end
Merge Hash value with existing Hash value.

 merge!(val)
 merge!(key, val)
 merge!(key1, key2, val)
 merge!([key], val)
 merge!([key1, key2], val)