Drag/drop of "text/plain" does not work, QMimeData::text() returns an empty string

    if (data.metaType().id() == QMetaType::QByteArray) {
        // see if we can convert to the requested type
        switch (typeId) {
        case QMetaType::QString: {
            const QByteArray ba = data.toByteArray();
            if (ba.isNull())         // <===============
                return QVariant();   // <=============== not QString()
            if (format == QLatin1String("text/html")) {
                auto encoding = QStringConverter::encodingForHtml(ba);
                if (encoding) {
                    QStringDecoder toUtf16(*encoding);
                    return QString(toUtf16(ba));
                }
                // fall back to utf8
            }
            return QString::fromUtf8(ba);
        }