Qt5 Connect Custom WindowClose Signal To A Different Window

I'm trying to connect a signal from one class to a slot in another class but when I do, my application crashes on startup. I read some other posts on here and the Qt forums that eluded to connecting custom signals as such but I think I'm connecting them wrong. Any help is greatly appreciated.

AdministrativeWindow.h

class AdministrativeWindow : public QMainWindow
{
    Q_OBJECT

    public:
        explicit AdministrativeWindow(QWidget *parent = 0);
        ~AdministrativeWindow();

    private slots:
        void on_actionExit_Administrative_Window_triggered();

    private:
        Ui::AdministrativeWindow *ui;

    signals:
        void windowClose();
};

AdministrativeWindow.cpp

void AdministrativeWindow::on_actionExit_Administrative_Window_triggered()
{
    emit windowClose();
    close();
}

MainWindow.cpp

connect(adminWindow, SIGNAL(windowClose()), this, SLOT(adminWindowClose()));

void MainWindow::on_ConfigureUsersBtn_clicked()
{
    if(adminWindow == NULL)
    {
        adminWindow = new AdministrativeWindow();
        adminWindow->show();
    }
    else if(adminWindow->isVisible())
    {
        adminWindow->activateWindow();
        adminWindow->showNormal();
    }
    else
    {
        adminWindow->show();
    }
}

void MainWindow::on_adminWindowClose()
{
    delete adminWindow;
    adminWindow = NULL;
}

You need to ensure that you're using valid adminWindow pointer on connect:

void MainWindow::on_ConfigureUsersBtn_clicked()
{
    if(adminWindow == NULL)
    {
        adminWindow = new AdministrativeWindow();
        connect(adminWindow, SIGNAL(windowClose()), this, SLOT(adminWindowClose()));
        adminWindow->show();
    }