This is unfortunate, because we jumped through a lot of hoops in the GUI layer to distinguish null (aka unset) values from empty values. This was to allow a user to specify one or the other, depending on if they want the prop to be unset (which tells the plugin to either specify null as the value or to not specify any value), or if they want the property to literally have "" as the value. This distinction is currently thrown away if the Server database is Oracle. The solution is probably to store some sort of special marker value in the DB to represent an empty string (e.g. a TAB character or some other character that's impossible to even enter via the GUI).