Can't parse null in arrays of Floats

[James Powell]

We use teh inbuilt NI code to parse arrays of numbers (for speed), but thus inherit it’s flaws. One is that it throws an error if the array has a null in it, and returns an array of all zeros (for ALL elements, nit just the null one!).

Desired behaviour is for null to become NaN.

[James Powell]

See tie in to #96