I solved it with using replace with regexp. However I am still confused why there was error with toUpperCase function called. There is only string as input as I need to dig this deeper.

Same problem

Yes but you cook pancakes one side at a time, so its not the number of pancakes you're cooking; it's the number of sides

hi how did you solve this problem

I'm having the same problem, perhaps you could make a specific statement that checks if it is this string and return false? But for real, not sure why this is happening.