issue comparing dates to empty string

I consider this a bug, since it used to work and it now does not, and it seems like a valuable shorthand.  At least it deserves mentioning in the changelog somewhere (I just looked through all of it)

In 4.0, you chould check to see if a datetime was not set with (Date='')
Now in 4.1, that fails.  I have found that the shorthand (Date='0') works.  Putting this change through all my source is an exhaustive process.

I think the first should also work, as it makes sense and is much easier than typing (Date='0000-00-00 00:00:00') everywhere its needed.