How forwarding on batch in the deploy sample (test.py)?

I am able to forward a single image with `f1 = model.get_feature(img)` in test.py in the deploy folder.
Now, I would like to process a batch of images.
I tried with `numpy.stack([img ... img])` obtaining, for example, a [2, 3, 112, 112] input ndarray, but now I have the following error:

`mxnet.base.MXNetError: Error in operator conv0: [19:16:34] C:\Jenkins\workspace\mxnet-tag\mxnet\src\operator\nn\convolution.cc:152: Check failed: dshp.ndim() == 4U (5 vs. 4) : Input data should be 4D in batch-num_filter-y-x`

Thanks in advance!