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
Looks like the length check is actually just being done to see if it's the first loop and doesn't actually correlate to the cleanedField that's being set. The code is a little confusing at first look.