Error when datetime is null

[danielgek]

if datetime var on that line is null(wich in javascript is also an object typeof null == "object"), this throws an error because getData on the if statement dont exists on null

will summit pr with fix soon

property-mixins/datetime-mixin.html

Line 567 in 61c3fc9

if ((typeof datetime === 'object' && datetime.getDate) || !isNaN(+datetime)) {