findChild возвращает nullptr

Какие варианты, кроме бага в Qt?

void ised_win::accept()
{
    m_session = m_edit->text();

    this->calculateCountofWidgetsAsync();

    if (grid)
    {
        while ( QWidget* w = grid->findChild<QPushButton*>() )
            delete w;
    }

    grid = new QVBoxLayout();
    for (int j = 0; j < m_countOfWidgets; ++j)
    {
        char buffer[3];
        itoa(j, buffer, 10);//to do
        auto bp = new QPushButton(buffer);
        grid->addWidget(bp);
    }
    vbox->addLayout(grid);
}//accept