Created attachment 108455 [details]
The main.qml file that makes it crash

$ qmlscene main.qml 
QObject::connect: invalid null parameter
Segmentation fault

the backtrace i have here is 
(gdb) bt
#0  0x00007fffd29ae9b1 in Kirigami::PlatformTheme::palette() const () from /usr/lib/libKF5Kirigami2.so.5
#1  0x00007fffd2bca640 in KQuickStyleItem::resolvePalette() () from /usr/lib/qt/qml/org/kde/qqc2desktopstyle/private/libqqc2desktopstyleplugin.so
#2  0x00007fffd2bca10c in KQuickStyleItem::initStyleOption() () from /usr/lib/qt/qml/org/kde/qqc2desktopstyle/private/libqqc2desktopstyleplugin.so
#3  0x00007fffd2bcae3d in KQuickStyleItem::sizeFromContents(int, int) () from /usr/lib/qt/qml/org/kde/qqc2desktopstyle/private/libqqc2desktopstyleplugin.so
#4  0x00007fffd2bcc14e in KQuickStyleItem::updateSizeHint() () from /usr/lib/qt/qml/org/kde/qqc2desktopstyle/private/libqqc2desktopstyleplugin.so
#5  0x00007fffd2bcda3e in KQuickStyleItem::setElementType(QString const&) () from /usr/lib/qt/qml/org/kde/qqc2desktopstyle/private/libqqc2desktopstyleplugin.so
#6  0x00007fffd2bd16d0 in KQuickStyleItem::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/qt/qml/org/kde/qqc2desktopstyle/private/libqqc2desktopstyleplugin.so
#7  0x00007ffff73df7a2 in ?? () from /usr/lib/libQt5Qml.so.5

Basically
  m_theme = static_cast<Kirigami::PlatformTheme *>(qmlAttachedPropertiesObject<Kirigami::PlatformTheme>(this, true));
is returning null