Script Check if a date & time field is empty

Hello,

I need to check whether a date & time field in the form I use is empty, and I need to do it with Java Script (it's necessary for a function I'm using, so business rules aren't an option).

I came up with this, but it isn't working (apparently, a date & time field isn't equaling null even though it appears to be empty):

if(Xrm.Page.getAttribute('new_dateandtime') == null) {...}

Does anyone know what an empty date & time field contains or could anyone help me in some other way? Thanks a lot!