docs: @Override
      public Iterator<byte[]> iterator() throws IOException {
          final Iterator<BytesKey> it = this.datas.keySet().iterator();
          return new Iterator<byte[]>() {
              @Override
              public boolean hasNext() {
                  return it.hasNext();
              }
  
  
              @Override
              public byte[] next() {
                  final BytesKey key = it.next();
                  if (null == key) {
                      return null;
                  }
                  return key.getData();
              }
  
  
              @Override
              public void remove() {
                  it.remove();
              }
          };
      }