inappropriate warnig "Empty filename passed to function" from QFileDialog

This code, under Linux, compiled with clang++4.0,

QDir dir(QDir::homePath());
    QFileDialog dlg(parent, caption, dir, filter);
    dlg.setAcceptMode(QFileDialog::AcceptOpen);
    dlg.setReadOnly(true);
    dlg.setProxyModel(new OpenFileProxyModel);
    dlg.setFileMode(plural ? QFileDialog::ExistingFiles : QFileDialog::ExistingFile);
    if (!dlg.exec())
        return {};
    return dlg.getFiles();

gives me a correct dialog with a left side pane that contains two entries,

• Computer,
• <my home dir>,

the latter being chosen by default. If I left-click on "Computer", a warning box pops up and says "Empty filename passed to function".

If I run the application under gdb and terminate by ^C when the warning appears, then I get this long backtrace:

.... [messaging trivia]
#10 0x00007ffff63f8094 in QMessageLogger::warning(char const*, ...) const () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#11 0x00007ffff6581e59 in () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#12 0x00007ffff64f8a5a in QDir::exists() const () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#13 0x00007ffff754c7bd in QFileDialogPrivate::_q_pathChanged(QString const&) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#14 0x00007ffff755218d in () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#15 0x00007ffff6625195 in QMetaObject::activate(QObject*, int, int, void**) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#16 0x00007ffff7559492 in QFileSystemModel::rootPathChanged(QString const&) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#17 0x00007ffff755d268 in QFileSystemModel::setRootPath(QString const&) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#18 0x00007ffff7543a55 in QFileDialog::setDirectory(QString const&) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#19 0x00007ffff7546e12 in QFileDialogPrivate::_q_enterDirectory(QModelIndex const&) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#20 0x00007ffff7546fd3 in QFileDialogPrivate::_q_goToUrl(QUrl const&) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#21 0x00007ffff755233d in () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#22 0x00007ffff6625195 in QMetaObject::activate(QObject*, int, int, void**) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#23 0x00007ffff75562d1 in () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#24 0x00007ffff7557249 in () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#25 0x00007ffff6625195 in QMetaObject::activate(QObject*, int, int, void**) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#26 0x00007ffff65a081a in QItemSelectionModel::currentChanged(QModelIndex const&, QModelIndex const&) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#27 0x00007ffff65a0b0e in QItemSelectionModel::setCurrentIndex(QModelIndex const&, QFlags<QItemSelectionModel::SelectionFlag>) ()
at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#28 0x00007ffff75a341c in QAbstractItemView::mousePressEvent(QMouseEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#29 0x00007ffff7391ccf in QWidget::event(QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#30 0x00007ffff74323de in QFrame::event(QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#31 0x00007ffff75a851b in QAbstractItemView::viewportEvent(QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#32 0x00007ffff65f561c in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#33 0x00007ffff73526a5 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#34 0x00007ffff735a3df in QApplication::notify(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#35 0x00007ffff65f5938 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#36 0x00007ffff73593b2 in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) ()
at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#37 0x00007ffff73ac4d3 in () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#38 0x00007ffff73aeb09 in () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#39 0x00007ffff73526cc in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#40 0x00007ffff7359e84 in QApplication::notify(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#41 0x00007ffff65f5938 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#42 0x00007ffff6b61603 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) ()
at /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#43 0x00007ffff6b630d5 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) ()
at /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#44 0x00007ffff6b3b03b in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
at /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5
#45 0x00007fffefbe720b in () at /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#46 0x00007ffff65f3b6a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#47 0x00007ffff753f8b7 in QDialog::exec() () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#48 0x00000000005361e2 in file_dialog::queryImportFileNames(QWidget*, QString const&, QDir&, QString const&, bool) (parent=<optimized out>, caption=..., dir=..., filter=..., plural=<error reading variable: access outside bounds of object referenced via synthetic pointer>)
at /G/Steca/gui/dialogs/file_dialog.cpp:142
.... [my app trivia]