Currently semantic properties all display a warning message when they're given a null value (e.g., [[Has country::]]). That makes sense if all properties are hand-coded, but if a site uses semantic templates, it could easily end up with many blank values.  Each of those gets a little warning flag, which could make many people think that something horrible has happened. Of course, an administrator can choose to not have warnings displayed, but many don't know how to do that, and sometimes it's useful to see the real error messages. Can warnings for null values be removed? A null value for a number just doesn't strike me as invalid data in the same way that, say, a value of "abcd" would be; I believe most relational databases, for example, allow null values for any type by default.