Error occurs when running test_pre_process.py for alignment

[czHappy]

(python367) root@d01acfa5ae2d:~/matting/Background-Matting# python test_pre_process.py -i sample_data/input Traceback (most recent call last): File "test_pre_process.py", line 108, in back_align = alignImages(back, image,mask) File "test_pre_process.py", line 51, in alignImages mask_rep1=np.logical_and(mask_rep , masksDL[...,0]==255) TypeError: 'NoneType' object is not subscriptable

I don't know why. Please tell me if someone knows how to solve it, thanks.