some fixes

src/EventManager.js

@@ -1427,7 +1427,7 @@ Calendar.prototype.buildBusinessGroup = function(wholeDay, input, rangeStart, ra
 		return this._buildBusinessGroup(wholeDay, input, true, rangeStart, rangeEnd);
 	}
 	else {
-		return [];
+		return new EventInstanceGroup([]);
 	}
 };
 

src/models/SingleEventDefinition.js

@@ -1,5 +1,5 @@
 
-var SingleEventDefinition = EventDefinition.extend({
+var SingleEventDefinition = EventDefinition.extend({ // TODO: mix-in some of EventInstance's methods?
 
 	start: null,
 	end: null,