QGIS » QGIS Application

I am trying to display features list on my own QAbstractTableModel.
By now it can sort columns just fine when all rows contains data. But whenever the column contains NULL/empty values the QgsVectorLayer::getFeatures method crash the application.

Code:
QgsFeatureRequest req;

req.addOrderBy(mLayer->attributeDisplayName(column), order == Qt::AscendingOrder);

QgsFeatureIterator it = mLayer->getFeatures(req);

QgsFeature feature;
long row = 0;
while (it.nextFeature(feature)) {
mRowToFeatureId[row++] = feature.id();
}