to_value(NAN) should be null

[dtolnay]

extern crate serde_json;

fn main() {
    let value = serde_json::to_value(::std::f64::NAN);
    println!("value: {}", value);
    println!("value.is_null(): {}", value.is_null());
}

Expected:

value: null
value.is_null(): true

Actual:

value: null
value.is_null(): false

[traviskaufman]

I can look into this.

Looks like serializing Value::F64(_) simply proxies to serialize_f64(v), where it should really check for FpCategory::{Nan, Infinite}, as serialization only works for finite values (https://tc39.github.io/ecma262/#sec-serializejsonproperty).