Change detection using Siamese network

I have been trying to find a good way to do a change detection with some images, I have found the following SNUNet paper witht heir github https://github.com/likyoo/Siam-NestedUNet, but when trying to use it I am always getting a blank output as a segmentation map, what did I do wrong? here is a link for my colab. thanks https://colab.research.google.com/drive/1h77eFWXUqTroShuVHueCrejp3F-t9wpm?usp=sharing