.
├── pom.xml
 ── src
     └── main
          ├── java
          │     └── tutorials
          │           ├── App.java
          │           ├── PrimaryController.java
          │           └── SecondaryController.java
          └── resources
                  └── tutorials
                          ├── primary.fxml
                          └── secondary.fxml

<resources>
        <resource>
            <directory>src/main/resources/tutorials</directory>
        </resource>
    </resources>

package tutorials;

@Override
public void start(Stage stage) throws IOException {
    GridPane grid =FXMLLoader.load(getClass().getResource("src/main/resources/primary.fxml"));
    Scene scene = new Scene(grid);
    stage.show();
}

Caused by: java.lang.NullPointerException: Location is required.