The method getLIstenerClass on ListenerInfo doesn't return the same type that the constructor takes. Look at https://github.com/undertow-io/undertow/blob/1.4.x/servlet/src/main/java/io/undertow/servlet/api/ListenerInfo.java#L65 vs how servlet info works https://github.com/undertow-io/undertow/blob/1.4.x/servlet/src/main/java/io/undertow/servlet/api/ServletInfo.java#L130

It should be reflecting back the constructor type.