NaN marshaling issue in setup() method

[olegbespalov]

Brief summary

Currently, if data that is going to return from the setup method contains a NaN value, k6 will fail with the error:

ERRO[0000] error marshaling setup() data to JSON: json: unsupported value: NaN

But for instance, marshaling an object that contains NaN in other places doesn't cause such an error.

Also, since by default, we marshal NaN as null, it's hard to figure out which property causes the issue for users.

For example:

let data = {x: null, y: NaN}
console.log(data)

will output to logs as:

INFO[0000] {"x":null,"y":null}                           source=console

So ideally, we should either improve the error message or fix the current behavior (e.g. treat the NaN as null)

Initially raised in community forums.

k6 version

v0.41.0

OS

linux/amd64

Docker version and image (if applicable)

No response

Steps to reproduce the problem

Given a script.js

export function setup() {
   return {y: NaN}
}

export default (data) => {
   console.log(data)
}

k6 run script.js

Expected behaviour

k6 runs as it should or explicitly say what's wrong.

Actual behaviour

ERRO[0000] error marshaling setup() data to JSON: json: unsupported value: NaN

[na--]

Somewhat connected to #2579?