Почему OpenViewerFX.loadPDF возвращает исключение нулевого указателя?

Question

В openviewerFX, когда я вызываю JFileChooser для сохранения моего PDF, он сохраняет, но сразу после этого предполагается открыть окно BaseViewerFX и отобразить указанный сохраненный PDF. Однако когда я запускаю программу, JFileChooser запускается, сохраняет, а затем, когда приходит время вызвать метод.loadPDF, он возвращает исключение нулевого указателя, даже если файл инициализирован в блоке if. Ошибка (ы) заключаются в следующем:

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(Unknown Source)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Node.fireEvent(Unknown Source)
    at javafx.scene.control.Button.fire(Unknown Source)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Scene$MouseHandler.process(Unknown Source)
    at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
    at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(Unknown Source)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.notifyMouse(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.Trampoline.invoke(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
    ... 53 more
Caused by: java.lang.NullPointerException
    at org.jpedal.examples.baseviewer.BaseViewerFX.start(Unknown Source)
    at fbla.rahulshah.database.dataManipulation.PDFCreationAndViewerLauncher.createDebtorPDF(PDFCreationAndViewerLauncher.java:53)
    at fbla.rahulshah.database.view.MainScreenController.generateDebtReport(MainScreenController.java:114)
    ... 62 more
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Qt: Untested Windows version 10.0 detected!
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
    at org.jpedal.examples.baseviewer.BaseViewerFX.openFile(Unknown Source)
    at org.jpedal.examples.baseviewer.BaseViewerFX.loadPDF(Unknown Source)
    at org.jpedal.examples.baseviewer.BaseViewerFX$7$1.run(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$null$173(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(Unknown Source)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Как вы можете видеть, это дает мне исключение нулевого указателя вместе с этой странной непроверенной вещью QT (я игнорирую это, потому что я посмотрел, что это было, и это, по-видимому, не важно). Даже когда я пытаюсь открыть его с помощью кнопки Открыть в окне BaseViewerFX, он делает то же самое. Я понимаю, что исключения nullPointerException являются чем-то, что может быть легко исправлено и вызвано тем, что переменная не инициализируется, но переменная инициализируется внутри блока if, в котором она была создана. Извлечение ее из блока if тоже ничего не делает. Вот код, чтобы увидеть для себя:

public void createDebtorPDF() throws Exception {
File file;
        JFileChooser fileChooser = new JFileChooser();
        ArrayList<StudentData> listOfDebtors = new ArrayList<StudentData>();
        int i = 0;


        listOfDebtors = StudentData.getListOfDebtors(i, listOfDebtors);

        PDDocument debtorDoc = new PDDocument();
        PDPage page = new PDPage();
        debtorDoc.addPage(page);
        createPDF(debtorDoc, page, i, listOfDebtors, i);



        Stage pdfStage = new Stage();
        BaseViewerFX baseViewer = new BaseViewerFX();


        if (fileChooser.showSaveDialog(fileChooser) == JFileChooser.APPROVE_OPTION) {

            file = fileChooser.getSelectedFile();
            file = checkFileName(file);

        file = fileChooser.showSaveDialog(null);
        file = checkFileName(file);
        baseViewer.init();
        debtorDoc.save(file); 
        pdfStage.setScene(baseViewer.setupViewer(600, 400));
        baseViewer.setupViewer(600, 400);

        pdfStage.show();
        baseViewer.loadPDF(file);
        baseViewer.start(pdfStage);
        debtorDoc.close();

        }
    }