@XSGeek - because null is null, 9 is a number, positive or negative infinity is a number, "foobar" is Not a Number, {some: "object"} is Not a Number.

(casing because articles don't get capitalized?)

@XSGeek - null is both null and Not a number. It's also not a string, and not equal to null (sometimes, but that's a hotly debated topic best left to mathematicians who've never coded). Null /is/ null, but you can't add 9 to a null, except when some languages allow it, but other times you can add null to 9, but not always because other languages don't allow that, but quite often you can add null to "9", and some languages will terminate it there, others will throw an error and... and... and...

@XSGeek - yeah... it's just one of those things... like learning that 1+1.0 = 2.00000000000003.