public void initRootLayout() {
        try {
            // Load root layout from fxml file.
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainApp.class.getResource("../views/FXML/Root.fxml"));
            rootLayout = (BorderPane) loader.load();
            [...]

.
├── out
    ├── artifacts
        └── LagerGUI
            ├── LagerGUI.html
            ├── LagerGUI.jar
            └── LagerGUI.jnlp
    ├── logs
        └── log.txt
    └── production
        ├── Controllers
        ├── Logger
        ├── MainApp
        ├── META-INF
        ├── structs
        └── views


├── src
|   ├── MainApp
        └── MainApp.java
    └── views
        ├── Controllers
        └── FXML
            └──Root.FXML

[...]
Caused by: java.lang.IllegalStateException: Location is not set.
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2434)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2409)
    at MainApp.MainApp.initRootLayout(MainApp.java:226)
    at MainApp.MainApp.start(MainApp.java:213)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$106(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$119(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$117(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$118(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication.lambda$null$450(GtkApplication.java:139)
    ... 1 more
Exception running application MainApp.MainApp