Adding IsNaN method

[mschmitz2]

Mass m = Mass.NaN;

Can now do

bool test = m.IsNaN();

instead of

bool test = double.IsNaN(m.SI);

[MadsKirkFoged]

Looks good! Good job making small, easy to read commits! and for remembering to create/change unit tests.

[MadsKirkFoged]

You could upgrade you solution with this if you want.

    public static bool IsNaN(this BaseUnit a)
    {
        if (a is null)
            return false;

        //return double.IsNaN(a.Value); // TODO: avoid using deprecated .Value here
        //return double.IsNaN(a.GetValueAsDouble(UnitSystemExtensions.UnitsystemForDouble));
        //return double.IsNaN(a.As(UnitSystemExtensions.UnitsystemForDouble));
        return a.NEWValue.IsNaN;
    }

[mschmitz2]

Oh, right, I had overlooked that. Makes way more sense