I assumed that in JS, the acceptable "None" output would be "undefined". Is it wrong to assume that?

Also: instruction say to create a function called first_non_repeating_letter then creates a function called firstNonRepeatingLetter.

JS version: Instructions say the valid output for no unique letters is "" or None. There is no example of what they mean by "None" anywhere. The instructions say to look at the test cases for examples; the test cases provided do not include any cases without any unique letters.

I did it in whole number seconds (no decimals for the seconds) and didn't convert until the very end. I still got a rounding error on generally 1-3 of the final tests. I kept hitting the "Attempt" button until it was 0 - which eventually worked.