LookupFilter in GPUImage3 throwing error (iOS)

Question

when i'm using LookupFilter from GPUImage3, it is working totally fine in renderview for displaying image. But for saving image, it's throwing error "Unexpectedly found nil while unwrapping an Optional value". Here is my code :

   effect = LookupFilter()

   effect.lookupImage = PictureInput(image: UIImage(named: "effect1")!) // UIImage is valid

   effect.intensity = 1
    
   let filteredImage = originalImage?.filterWithOperation(effect)

could anyone help to find the solution ??