NullPointer при попытке доступа к Java ArrayList<User>, который НЕ является нулевым

У меня есть ArrayList в моем UserController, в котором хранятся все мои экземпляры User.

Я могу использовать свой setUserList для успешной установки ArrayList, поскольку я могу прокручивать и печатать имя пользователя с помощью currentUser.getFirstName()

Я запускаю функцию входа в систему с помощью кнопки JavaFX и получаю исключение NullPointer, когда просто пытаюсь напечатать размер ArrayList, который ранее имел размер 1, и печатал имя пользователя.

Пользовательский контроллер:

 public class UserController {
    public ArrayList<User> userList;  //should contain one user thomas but gives null pointer
    //static ArrayList<User> userList;  //this does not return a null pointer

    public void setUserList(ArrayList list){
        userList = list;
        for (User user : userList) {
            User currentUser = (User) user;
            String firstName = currentUser.getFirstName();
            System.out.println("Users in the UserController: " + firstName); //prints the user thomas
        }
    }

    public void login(){
        try {
            System.out.println(userList.size()); //null pointer
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

UserInterface, содержащий метод входа в систему

    public class UserInterface extends Application {

    User loggedInUser;
    UserRepo userRepo = new UserRepo();
    UserController userController = new UserController();
    Connection conn;

    //login.fxml
    @FXML
    public TextField InputEmailAddress;  
    @FXML
    public TextField InputPassword;  

    @Override
    public void start(Stage stage) throws Exception {

        String connectionURL = "jdbc:derby://localhost:1527/gymManager";
        String userName = "root";
        String userPassword= "root";
        try {

            conn = DriverManager.getConnection(connectionURL, userName, userPassword);
            if (conn != null){
                System.out.println("Connected to the database");
                ArrayList<User> list = userRepo.read(conn);

                userController.setUserList(list); //here is where I set the ArrayList<Users> in the USerController

                Parent root = FXMLLoader.load(getClass().getResource("login.fxml"));

                Scene scene = new Scene(root);

                stage.setScene(scene);
                stage.show();
            }

        } catch(SQLException e){
            System.out.println("Exception:" + e.toString()); 
        }  

    }

    public static void main(String[] args) {
        launch(args);
    }

    public void login(ActionEvent event) throws Exception{

        userController.login();

    }



}

логин.fxml

<?xml version = "1.0" encoding = "UTF-8"?>

<?import java.lang.String?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.image.Image?>
<?import javafx.scene.image.ImageView?>
<?import javafx.scene.layout.Pane?>
<?import javafx.scene.text.Font?>

<Pane maxHeight = "-Infinity" maxWidth = "-Infinity" minHeight = "-Infinity" minWidth = "-Infinity" prefHeight = "720.0" prefWidth = "1080.0" styleClass = "main-pane" xmlns:fx = "http://javafx.com/fxml/1" fx:controller = "classmanager.UserInterface">
   <children>
      <Button fx:id = "loginButton" layoutX = "583.0" layoutY = "451.0" onAction = "#login"  mnemonicParsing = "false" prefHeight = "56.0" prefWidth = "191.0" text = "Log In">
         <font>
            <Font name = "Montserrat Regular" size = "13.0" />
         </font>
         <styleClass>
            <String fx:value = "white-btn" />
            <String fx:value = "bg-blue" />
            <String fx:value = "rounded-btn" />
         </styleClass></Button>
      <Button layoutX = "784.0" layoutY = "451.0" mnemonicParsing = "false" prefHeight = "56.0" prefWidth = "158.0" text = "I'm new here">
         <font>
            <Font name = "Montserrat Regular" size = "13.0" />
         </font>
         <styleClass>
            <String fx:value = "outline-btn" />
            <String fx:value = "rounded-btn" />
         </styleClass></Button>
      <Button layoutX = "563.0" layoutY = "514.0" mnemonicParsing = "false" prefHeight = "38.0" prefWidth = "231.0" styleClass = "transparent-btn" text = "I've forgotten my password">
         <font>
            <Font name = "Montserrat Regular" size = "13.0" />
         </font></Button>
      <Label layoutX = "581.0" layoutY = "273.0" prefHeight = "18.0" prefWidth = "411.0" text = "Book classes and manage your membership details here" textFill = "#9a9a9a">
         <font>
            <Font name = "Montserrat Regular" size = "14.0" />
         </font>
      </Label>
      <Label layoutX = "577.0" layoutY = "180.0" prefHeight = "18.0" prefWidth = "353.0" text = "Welcome to the" textFill = "#1a73b5">
         <font>
            <Font name = "Montserrat Medium" size = "30.0" />
         </font>
      </Label>
      <Label layoutX = "577.0" layoutY = "217.0" prefHeight = "50.0" prefWidth = "411.0" text = "Village Hotel Gym" textFill = "#1a73b5">
         <font>
            <Font name = "Montserrat Medium" size = "40.0" />
         </font>
      </Label>
      <ImageView fitHeight = "730.0" fitWidth = "544.0" layoutX = "-25.0" layoutY = "-4.0" pickOnBounds = "true" preserveRatio = "true">
         <image>
            <Image url = "@../login-banner.jpg" />
         </image>
      </ImageView>
      <TextField fx:id = "InputEmailAddress" layoutX = "581.0" layoutY = "325.0" prefHeight = "50.0" prefWidth = "386.0" promptText = "Email address" styleClass = "login-input">
         <opaqueInsets>
            <Insets left = "20.0" />
         </opaqueInsets>
         <font>
            <Font name = "Montserrat Regular" size = "13.0" />
         </font>
      </TextField>
      <TextField fx:id = "InputPassword" layoutX = "581.0" layoutY = "384.0" prefHeight = "50.0" prefWidth = "386.0" promptText = "Password" styleClass = "login-input">
         <opaqueInsets>
            <Insets left = "20.0" />
         </opaqueInsets>
         <font>
            <Font name = "Montserrat Regular" size = "13.0" />
         </font>
      </TextField>
   </children>
</Pane>

Я просто не могу понять, почему один метод (setUserList) в классе UserController скажет мне, что ArrayList содержит 1 пользователя, а другой (логин) вернет NullPointer

Спасибо за любые советы