GRADCAM Error

Deep Learning
1 
interp.GradCAM(5)

TypeError                                 Traceback (most recent call last)
<ipython-input-35-d8d31c26ab27> in <module>()
----> 1 interp.GradCAM(5)

/usr/local/lib/python3.6/dist-packages/fastai/vision/learner.py in _cl_int_gradcam(self, idx, ds_type, heatmap_thresh, image)
    147     acts  = hook_a.stored[0].cpu() #activation maps
    148     if (acts.shape[-1]*acts.shape[-2]) >= heatmap_thresh:
--> 149         grad = hook_g.stored[0][0].cpu()
    150         grad_chan = grad.mean(1).mean(1)
    151         mult = F.relu(((acts*grad_chan[...,None,None])).sum(0))

TypeError: 'NoneType' object is not subscriptable
2

Check if the mode is unfreeze before saving to export.pkl