How to use void and number type in functions with guard-clauses

Problem: I’m trying to write a simple function with a guard-clause in addition to returning a value with type: number, but ESLint is telling me "void is only valid as a return type or generic type variable"

P.S: I don’t know why ESLint is throwing me this, if I use void as a return type for guard-clause …

Code:

function addTwoNumbers(one: number, two: number): void | number {
  if (one < 0 || two < 0) return;
  return one + two;
}

const result = addTwoNumbers(-5, -5);
console.log(result);

I’ve tried specifying only number type to the function, but in this case ESLint is telling me "Type undefined is not assignable to type number"

>Solution :

Instead of void you need to put undefined. By default, an empty return statement will return undefined.