DDF-894 Added propertyIsNull support to the SolrFilterDelegate

-kind of odd to get this to work.  First you come in without a field type so we have to do so using the getAnonymousField() method.  Than we have to use the negative queries to actually get the results we need. (*:* -fieldName:[* TO *]) is the magic sause to get this to work.  For details on how this works, visit the url below.
-http://stackoverflow.com/questions/17044661/how-to-filter-search-by-values-that-are-not-available/17045097#17045097
the original length check was to catch the first iteration of the foreach loop.  However, since I'm using StringUtils.join() I get the functionality I need without having to do this check.