prevent mquat from looking for indexes it cannot build.

jastadd-mquat-eris/src/main/java/de/tudresden/inf/st/mquat/eris/coupling/ERISAttribute.java

@@ -26,6 +26,7 @@ public class ERISAttribute {
     typeLength = jsonObject.getInt("typeLength");
     unique = jsonObject.getBoolean("unique");
     allowIndex = jsonObject.getBoolean("allowIndex");
+    allowIndex = allowIndex && notNull && notUndefined;
     this.container = container;
   }