A common issue I've seen is more the return is replaced with a print statement. As a result, their code "appears" to working because they're still seeing the ri

A common issue I've seen is more the return is replaced with a print statement. As a result, their code "appears" to working because they're still seeing the right values appear in their console when they run the code. If the function's returned value doesn't get used somewhere else, then they don't see where the issue is until points are deducted.