Can field() be requested in a QWizard before initialization?

[RDiGuida]

I am calling a QWizardPage from a function in the MainWindow

void MainWindow::NoiseFilling()
{
    QWizard *wiz = new QWizard;
    NoiseFillPage *pg = new NoiseFillPage(&data);
    wiz->addPage(pg);
    wiz->setWindowTitle("Noise Filling");
    wiz->setOption(QWizard::NoBackButtonOnStartPage);

    QVBoxLayout *ly = new QVBoxLayout;
    QLabel *pb = new QLabel;
    ly->addWidget(wiz);
    ly->addWidget(pb);

    connect(wiz,&QDialog::accepted,[&](){data.NoiseFill(wiz->field("percent").toInt(),wiz->field("factor").toString());});  //problem here
    connect(wiz,&QDialog::accepted,[&](){textEdit->setText("Dataset noise filled.\n");});
    delete frame->layout();   // delete previous layout
    frame->setLayout(ly);
    wiz->show();
}

and the constructor of the WizardPage looks like that

NoiseFillPage::NoiseFillPage(DataFrame* df,QWidget* parent)
    : QWizardPage(parent)
{
    box = new QComboBox;
    lab = new QLabel("Metadata factor");
    lab_2 = new QLabel("% of missing values threshold to fill");
    sb = new QSpinBox;

    box->insertItem(0,*(df->className));
    box->insertItems(1,*(df->namesMetaData));

    sb->setMaximum(100);
    sb->setMinimum(30);
    sb->setValue(100);

    QGridLayout *ly = new QGridLayout;
    ly->addWidget(box,0,0);
    ly->addWidget(lab,0,1);
    ly->addWidget(sb,1,0);
    ly->addWidget(lab_2,1,1);

    setLayout(ly);

    registerField("factor",box);
    registerField("percent",sb);
}

I receive a segmentation fault when I accept (and therefore close) the dialog of the one-page wizard. The debugger stops on the connect instruction making me believe that the problem arises because I am requesting two fields which are not initialised in compile-time. It is also true that this connection would be made at run time so I am very confused. After narrowing down the issue it seems that it has to do with the call wiz->field("percent"). Does anybody have an idea of what is going on?