How to send NaN over res.json() with express?

I’m currently handling a simple Typescript API with express who handle simple tasks.
For one case, I need to send a property which is of type:

export Toto = {
  ...
  rate: number | null
  ...
};

But the rate property may also be NaN. In fact, this property is a mere number with 2 special value: null and NaN.

The issue is even if I explicitly send NaN at the very end, my front end will receive null. After some investigation I discovered JSON.stringify() was replacing all my NaN entries by null, but I need both of them.

I do know a simple:

JSON.stringify(obj, (k, v) => Number.isNaN(v) ? "NaN" : v)

can solve this problem, but how to adapt it to express.js ?

I’m answering using:

res.status(200).json(obj);