Allowing assert.deepEqual to check NaN values for equality

An Object may have NaN as one of its property values.  NaN doesn't compare directly to itself, so isNaN() must be used instead.
Why am I looking for Number.isNaN()?  Seems like the difference between a person holding up their pants with a rope versus a belt.  The confusing behavior of the naked isNaN() is related to it coercing its parameter into a Number to perform the check.  In this line, we've already checked for its typeof being a Number.