Return-statement with no value

[Stanfillirenfro]

Hello!

I am facing a problem.
I want to use the conten of a file bt I have to check first if the file is opened.
I am receiving th efollowing error message: "return-statement with no value, in function returning 'QStringList"

My question: How to stop the process if the file can not be opened, since "return-statement does not work here?
break-statement can be used only in a loop.

Here is my code.

QStringList myWindow::open(QString &fileName)
{
    QFile file(fileName);
 
    if(!file.open(QIODevice::ReadOnly))
    {
        QMessageBox::critical(this, "Warning", "Open a file please");
        return;
    }
 
// I do something here
}

QStringList myWindow::open(QString &fileName)
{
    QFile file(fileName);

    if(!file.open(QIODevice::ReadOnly))
    {
        QMessageBox::critical(this, "Warning", "Open a file please");
        return;
    }

// I do something here
}

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Many thanks in advance.