code: @Override
      public NDArrayMessage doGetUpdate(int index) {
          byte[] key = ByteBuffer.allocate(4).putInt(index).array();
          try {
              UnsafeBuffer unsafeBuffer = new UnsafeBuffer(db.get(key));
              return NDArrayMessage.fromBuffer(unsafeBuffer, 0);
          } catch (RocksDBException e) {
              throw new RuntimeException(e);
          }
      }
docs: A method for actually performing the implementation
  of retrieving the ndarray
  
  @param index the index of the {@link INDArray} to get
  @return the ndarray at the specified index