mmm I don't understand why.

My goal here is to have 2 versions of the function: one with 3 arguments, one with 4 arguments.
When there are 3 arguments, I want that the "expected" value is the 3rd parameter.
When there are 4 arguments, I want that the "expected" value is the 4th parameter.

I could also use `arguments.length` if you prefer.