Investigate NaN in spec

[sffc]

From @FrankYFTang:

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Also in the README.md it said

Ranges to infinity are supported, but if either value is NaN, an error is thrown. (#12)

nf.formatRange(500, 0/0); // RangeError

But I have a hard time figuring out where in the spec to throw the NaN now.
I don't think ToIntlMathematicalValue will throw if the value is NaN right?
https://tc39.es/proposal-intl-numberformat-v3/out/numberformat/diff.html#sec-partitionnumberrangepattern

If x is a non-finite Number or y is is a non-finite Number, throw a RangeError exception.

What is the definition of "non-finite Number" ?
Is NaN a "non-finite Number" ? I cannot tell
https://tc39.es/proposal-intl-numberformat-v3/out/numberformat/diff.html#sec-partitionnumberpattern
surely won't throw if NaN because

If x is NaN, then
Let n be an implementation- and locale-dependent (ILD) String value indicating the NaN value.