Patch to show Entity Reference Values (Titles, UserNames) and also a Filter for NULL values which return broken arrays

I had an issue whereby Entity Reference fields were showing the entity_id instead of the entity_title/name, etc. Here is a patch that fixes that. Also, Organic Groups is using entity_reference widget, but does not use its storage, so this presents an issue with NULL values. I have also added a filter to the options for NULL and Empty values.