I also have a news list that I added a year filter to that has a list of 4 digit years and an "All" option. The parameter I am using is "year=". If "year=#" where # is some 4 digit number that is greater than or equal to 1753 then the widget will render. If it is a number less than that or alphanumeric, then the widget will not render. I have a breakpoint in the page load method in the code-behind of the widget template that is never hit in these situations.
All you have to do to reproduce this issue is to drop a News list on a page and set the url evaluation mode to QueryString. Apparently this is a built in feature but I hit the googles and couldn't find it.