OpenCV error - cv2.error: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor

Usually if you are using an input video file - the name or directory is wrong
or if you are using a camera feed - maybe your integrated camera isn't working- I ended up using a USB camera and changing the video capture in the code from 0 to 1. I hope this can work for testing, I really want to get my integrated camera working on my Raspberry Pi.