added assert

src/magic/model/choice/MagicPlayChoiceResult.java

@@ -20,15 +20,17 @@ public class MagicPlayChoiceResult implements MagicMappable {
 	public Object map(final MagicGame game) {
 		if (this==PASS) {
 			return PASS;
-		}
+		} else {
     		return new MagicPlayChoiceResult((MagicSource)source.map(game),activation);
         }
+	}
 	
 	@Override
 	public String toString() {
 		if (this==PASS) {
 			return "pass";
 		} else {
+            assert source != null;
 			return source.getName();
 		}
 	}