because null === null evaluates to true
if I'm understanding your question correctly

Combine so many ternary operators in 1 line so bad, bro

I wrote my solution of ~30 lines and i thought it was short, but now i am shocked :)

Read the posts below. Like this one: https://www.codewars.com/kata/reviews/55908ab5932c2fc59f000070/groups/55c8b47c16ffe086d7000056#6312e85473f6480018781578

Please use the spoiler flag and appropriate formatting when posting code. See here: https://docs.codewars.com/training/troubleshooting/#post-discourse

The problem is that I can't use Number?

You can use any function as long as you implement the correct validation logic. Usage of Number is not restricted for this kata.

Everything works fine in my VS Code.

Your code is definitely incorrect if it fails for basic cases like "1234". You must be incorrectly (locally) testing your function.