why test psnr is nan

Please provide more information, such as which dataset for testing and which version of MegEngine. In my case, this test script worked well and the result was 39.765.
thanks for your answer.my MegEngine is 1.5 and the test data is the val set of sidd.
After installing MegEngine=1.5, your results still cannot be reproduced. Please check whether the image pair to be calculated is correct, and check whether nan appears in each image pair or only a few pairs.
At first,I meet the error in this script dataset.py ,"no module named nori2",so I just delete this row of the original code because nori2 cannot be installed by pip. May be this reason?
Thanks for pointing out this error, I have deleted these external packages. But I don't think this is the reason why the output is nan and please clone this project again and test again. I provide my numerical packages for reference: MegEnginee == 1.5.0 numpy. == 1.19.5 opencv-python == 4.5.3.56 scikit-image == 0.17.2 scipy == 1.5.4 six == 1.16.0