'NoneType' object has no attribute '__getitem__' when using ROS image_geometry

I was trying to convert pixel to spatial coordinates when I found the package image_geometry. I initialized it, and called the desired function, taken from the API. Here's what I did:

import image_geometry
from image_geometry import PinholeCameraModel

self.img_geo = PinholeCameraModel()
(r_x,r_y,r_z) = self.img_geo.projectPixelTo3dRay((359,285))
print(r_x)

Obviously the self.img_geo is in my init function and then later on I use the projection function, and then get that error. Any ideas what's wrong?