NPE when accessing protected method from subclass clone

@groovy.transform.CompileStatic
class LazyMap implements Map<String,Object> {

    @Delegate protected Map<String,Object> target

    LazyMap() {
        target = new HashMap<>()
    }
}

@groovy.transform.CompileStatic
class TaskConfig extends LazyMap implements Cloneable {

    TaskConfig() {  }

    TaskConfig clone() {
        def copy = (TaskConfig)super.clone()
        copy.target = new HashMap<>(this.target)
        return copy
    }
}