Why not letting the error occur in the debugger?
It's a shame that the instructor does not let the error actually occur in the debugger. Instead, he fixes the problem before any error pops in the debugger. That does not make sense!
Thanks for reaching out.
The instructor has likely addressed the mistake in advance to avoid prolonging the lesson by going through the debugging process once more. Nonetheless, he does highlight that the upcoming step is expected to result in an error. You are encouraged to replicate this error on your own and then apply the correction.