Unable to remove a GridDragSource

[PaulLaganke]

• Vaadin Framework version
• Browser version
• Description of the bug
• Minimal reproducible example

---

Famework version: 8.8.2
Browser Version: Fireforx 67.0

In my case i tried to create a grid with an added GridDragSource component, until this point it works like expected. In this situation i need to disable the dragging, i tried by removing the component, this results in a thrown nullpointer exception caused by the parent (which is null).

(removing process, error at dragsource.remove();)
`
public class UI extends com.vaadin.ui.UI {

private GridDragSource<String> dragsource;
private Grid<String> grid;

@Override
protected void init(VaadinRequest request) {
    List<String> list = new ArrayList<>();
    list.add("test1");
    list.add("test2");
    list.add("test3");
    list.add("test4");

    VerticalLayout content = new VerticalLayout();

    grid = new Grid<>();
    grid.setItems(list);
    grid.addColumn(String::toUpperCase).setCaption("content");

    dragsource = new GridDragSource<>(grid);
    dragsource.setEffectAllowed(EffectAllowed.MOVE);


    Button removeDragSource = new Button("remove");
    removeDragSource.addClickListener(e->{
        dragsource.remove();
    });
    content.addComponents(removeDragSource, grid);
    setContent(content);
}

}
`

(AbstractClientConnector -> parent (grid) is set null, might be not correct)
`
@OverRide
public void removeExtension(Extension extension) {
if (extension.getParent() != this) {
throw new IllegalArgumentException(
"This connector is not the parent for given extension");
}

    extension.setParent(null);
    extensions.remove(extension);
    markAsDirty();
}

Nullpointer Stacktrace:

java.lang.NullPointerException: null at com.vaadin.ui.components.grid.GridDragSource.remove(GridDragSource.java:261) ~[vaadin-server-8.8.2.jar:8.8.2] at de.hup.one.dragsourceDemo.UI.lambda$init$c097127e$2(UI.java:50) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202] at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:499) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.8.2.jar:8.8.2] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202] at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:116) ~[vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:445) [vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:410) [vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:274) [vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:90) [vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) [vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1602) [vaadin-server-8.8.2.jar:8.8.2] at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:445) [vaadin-server-8.8.2.jar:8.8.2] at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) [tomcat-embed-websocket-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.1.7.RELEASE.jar:5.1.7.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:836) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1747) [tomcat-embed-core-9.0.19.jar:9.0.19] at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.19.jar:9.0.19] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_202] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_202] at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.19.jar:9.0.19] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_202]

`