Fixed Event.Valueless#toString() to not display the null value

src/main/java/envoy/event/Event.java

@@ -42,5 +42,8 @@ public abstract class Event<T> implements Serializable {
 		private static final long serialVersionUID = -9019362144094097997L;
 
 		protected Valueless() { super(null); }
+
+		@Override
+		public String toString() { return this.getClass().getSimpleName(); }
 	}
 }