Error repainting a FlowPanel on an onDrop event widget

Hi,

I'm repainting all the content of a FlowPanel that have DraggableWidget<DockPanel>.
I don't know where the application return the error, because the error is internal of GWT libraries.
The error is caused in this code:

public static void loadArbre(HandlerManager eventBus) {
        List<FilaPanel> files = EditorView.getInstance().getFiles();
        FlowPanel panell = EditorView.getInstance().getPanell();
        files.clear();
        panell.clear();
       
        List<Fila> filesArbre = DRGUtils.getArbre().getElementRegistre(1).getElementNivell(1).getFiles();
       
        for(int idFila=0; idFila<filesArbre.size(); idFila++) {
            Fila fila = filesArbre.get(idFila);
            FilaPanel filaPanel = new FilaPanel(false, idFila+1);
            filaPanel.setWidth(FilaPanel.WIDTH_FILA + "px");
            filaPanel.recalculaEspaisWidgets(FilaPanel.WIDTH_FILA, FilaPanel.SPACING_FILA);
            files.add(filaPanel);
            panell.add(filaPanel);
            for(int idElement=0; idElement<fila.getElements().size(); idElement++) {
                Component component = fila.getElements().get(idElement);
                if(component instanceof Requadre) {
                    RequadrePanel requadre = new RequadrePanel("" + ((Requadre)component).getId(), false);
                    requadre.setFila(filaPanel);
                    filaPanel.addElement(idElement, requadre);
                    requadre.setHeight(FilaPanel.HEIGHT_FILA);
                    requadre.setEventBus(eventBus);
                    DRGUtils.inicialitzaFilesRequadre(((Requadre)component).getId());
                    for(int idFilaRequadre=0; idFilaRequadre<((Requadre)component).getFilesRequadre().size(); idFilaRequadre++) {
                        Fila filaRequadre = ((Requadre)component).getFilesRequadre().get(idFilaRequadre);
                        FilaRequadrePanel filaRequadrePanel = new FilaRequadrePanel(false, filaRequadre.getFilaID());
                        filaRequadrePanel.setWidth(FilaPanel.WIDTH_FILA + "px");
                        VariablePanel lastVariable = null;
                        for(int idVariable=0; idVariable<filaRequadre.getElements().size(); idVariable++) {
                            Component componentRequadre = filaRequadre.getElements().get(idVariable);
                            if(componentRequadre instanceof Variable) {
                                VariablePanel areaVariable = new VariablePanel("" + ((Variable)componentRequadre).getId(), false);                       
                                areaVariable.setInRequadre(true);
                                areaVariable.setRequadre(requadre);
                                areaVariable.setSizeInRequadre();
                                areaVariable.setFila(filaPanel);
                                areaVariable.setFilaRequadre(filaRequadrePanel);
                                areaVariable.setHeight(FilaPanel.HEIGHT_FILA);
                                areaVariable.setEventBus(eventBus);
                                if(idVariable==0) {
                                    requadre.onVariableDinsRequadre(areaVariable, requadre, filaRequadrePanel);
                                } else {
                                    requadre.onAfegirElementRequadre(areaVariable, lastVariable, filaRequadrePanel, AreesPanel.EAST, requadre);
                                }
                                lastVariable = areaVariable;
                            }
                        }
                    }
                } else if(component instanceof Variable) {
                    VariablePanel arees = new VariablePanel("" + ((Variable)component).getId(), false);
                    arees.setFila(filaPanel);
                    arees.setEventBus(eventBus);
                    filaPanel.addElement(idElement, arees);
                    arees.setHeight(FilaPanel.HEIGHT_FILA);
                }
            }
        }
    }

I think the cause is de clear of the object panell that is a FlowPanel. This method is called in the onDrop event of a object that contains the FlowPanel panell. So I think the error is because I clear an object on the event onDrop of the same object. I hope I explain correcty.
This is the exception:

Uncaught exception: java.lang.NullPointerException
    at gwtquery.plugins.draggable.client.events.DragContext.init(DragContext.java:104)
    at gwtquery.plugins.draggable.client.events.DragContext.<init>(DragContext.java:48)
    at gwtquery.plugins.draggable.client.events.AbstractDraggableEvent.<init>(AbstractDraggableEvent.java:41)
    at gwtquery.plugins.draggable.client.events.DragStopEvent.<init>(DragStopEvent.java:37)
    at gwtquery.plugins.draggable.client.Draggable$3.execute(Draggable.java:490)
    at com.google.gwt.core.client.impl.SchedulerImpl$Task$.executeScheduled$(SchedulerImpl.java:50)
    at com.google.gwt.core.client.impl.SchedulerImpl.runScheduledTasks(SchedulerImpl.java:180)
    at com.google.gwt.core.client.impl.SchedulerImpl.flushPostEventPumpCommands(SchedulerImpl.java:347)
    at com.google.gwt.core.client.impl.SchedulerImpl$Flusher.execute(SchedulerImpl.java:78)
    at com.google.gwt.core.client.impl.SchedulerImpl.execute(SchedulerImpl.java:138)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:242)
    at sun.reflect.GeneratedMethodAccessor44.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
    at java.lang.Thread.run(Thread.java:724)

Thanks in advanced,

David Martínez

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