It's the same as passing in 0. When Date is passed a number, I believe it treats it as a unix timestamp. In this case (0 or null), it'll be equal to Jan 1st, 1970.

However, I don't think there's any value you can pass to Date to have `dust.isEmpty` return true... think this will be an issue? Should we update `dust.isEmpty` to include an `instanceof Date` check and then a subsequent call to `.valueOf` or `.getTime`? Or maybe just update the last line to be `return (!value.valueOf());`?