While working on a project we get the error below. First we thought it had to do with calculated attributes, but after removing them the error still occurs. Does anyone know what this error is about and how we can avoid it? java.lang.NullPointerException: null at com.mendix.webui.actions.ActionUtil$.com$mendix$webui$actions$ActionUtil$$hasNoVirtualAttributes(ActionUtil.scala:65) at com.mendix.webui.actions.ActionUtil$$anonfun$buildSortMap$1.apply(ActionUtil.scala:41) at com.mendix.webui.actions.ActionUtil$$anonfun$buildSortMap$1.apply(ActionUtil.scala:38) at scala.collection.immutable.Range.foreach(Range.scala:160) at com.mendix.webui.actions.ActionUtil$.buildSortMap(ActionUtil.scala:38) at com.mendix.webui.actions.ActionUtil$.buildSortMap(ActionUtil.scala:31) at com.mendix.webui.actions.ActionUtil$.addSortExpressions(ActionUtil.scala:136) at com.mendix.webui.actions.client.XPathRetriever.retrieveWithSchema(XPathRetriever.scala:69) at com.mendix.webui.actions.client.RetrieveByXPathAction.execute(RetrieveByXPathAction.scala:36) at com.mendix.webui.requesthandling.ClientRequestHandler$$anonfun$handleRequest$1.apply$mcV$sp(ClientRequestHandler.scala:300) at com.mendix.webui.requesthandling.ClientRequestHandler$$anonfun$handleRequest$1.apply(ClientRequestHandler.scala:293) at com.mendix.webui.requesthandling.ClientRequestHandler$$anonfun$handleRequest$1.apply(ClientRequestHandler.scala:293) at com.mendix.core.session.Worker$$anonfun$receive$3$$anonfun$2$$anon$1.execute(ActionDispatching.scala:151) at com.mendix.util.classloading.Runner.doRunUsingClassLoaderOf(Runner.java:37) at com.mendix.core.session.Worker$$anonfun$receive$3$$anonfun$2.apply(ActionDispatching.scala:153) at scala.util.Try$.apply(Try.scala:191) at com.mendix.core.session.Worker$$anonfun$receive$3.applyOrElse(ActionDispatching.scala:147) at akka.actor.Actor$class.aroundReceive(Actor.scala:465) at com.mendix.core.session.Worker.aroundReceive(ActionDispatching.scala:140) at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516) at akka.actor.ActorCell.invoke(ActorCell.scala:487) at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:238) at akka.dispatch.Mailbox.run(Mailbox.scala:220) at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:393) at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)