JavaFX : java.lang.IllegalStateException: Location is not set

Question

I have an annoying problem in my JavaFX project : I want to open an other fxml file (in a new window) on a button click in my main window. Here is my code below :

import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

import java.net.URL;

public class Controller {

@FXML
public void newButton(ActionEvent event) throws Exception {
    try {
        URL fxmlLocation = getClass().getResource("/resources/new_wind.fxml");
        System.out.println(fxmlLocation);

        FXMLLoader fxmlLoader = new FXMLLoader();
        fxmlLoader.setLocation(getClass().getResource("/resources/new_wind.fxml"));

        Parent root1 = (Parent) fxmlLoader.load();
        Stage stage = new Stage();
        stage.setTitle("windows");
        stage.setScene(new Scene(root1));
        stage.show();
    } catch(Exception e) {
        e.printStackTrace();
    }
}

}

My file structure :

My main window is in sample.fxml, and the window I want to open is in resources folder (marked as resources folder in intellij) : "window.fxml".

When I try to click on this button, I got this error which refers to a path problem : "java.lang.IllegalStateException: Location is not set."

The line "System.out.println(fxmlLocation)" returns a null value indeed, so how to get the "correct" path for my new file ?

I precise that I got also an unknow class error in my window.fxml file, caused by this line : "fx:controller="Window".