SUMMARY
I search for a string like 'a b c d e f g h i j k l ...' or others but with this one it fails each time.

After adding my collection, with multiple duplicated file and a directory failing import (modification date 31 dec 1969).

Amarok crash

STEPS TO REPRODUCE
1.  Import lot of directories with a directory modified the 31 dec 1969 and multiple duplicates
2.  Search for some song title or string earlier
3.  Crash

OBSERVED RESULT
Crash

EXPECTED RESULT
Should not crash

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
Calling appendChild() on a null node does nothing.

Thread 1 "amarok" received signal SIGSEGV, Segmentation fault.
0x00007ffff783d0d0 in CollectionTreeItem::row() const () from /lib64/libamaroklib.so.1
(gdb) bt
#0  0x00007ffff783d0d0 in CollectionTreeItem::row() const () at /lib64/libamaroklib.so.1
#1  0x00007ffff7842380 in CollectionTreeItemModelBase::itemIndex(CollectionTreeItem*) const () at /lib64/libamaroklib.so.1
#2  0x00007ffff7842400 in CollectionTreeItemModelBase::parent(QModelIndex const&) const () at /lib64/libamaroklib.so.1
#3  0x00007ffff6274799 in QModelIndex::parent() const (this=0x11e9790) at ../../include/QtCore/../../src/corelib/itemmodels/qabstractitemmodel.h:443
#4  QSortFilterProxyModelPrivate::_q_sourceDataChanged(QModelIndex const&, QModelIndex const&, QVector<int> const&)
     (this=0xdcf670, source_top_left=<optimized out>, source_bottom_right=<optimized out>, roles=...) at itemmodels/qsortfilterproxymodel.cpp:1433
#5  0x00007ffff62d3f84 in doActivate<false>(QObject*, int, void**) (sender=0xaeda30, signal_index=3, argv=0x7fffffffd2f0) at kernel/qobject.cpp:3931
#6  0x00007ffff62cd55f in QMetaObject::activate(QObject*, QMetaObject const*, int, void**)
    (sender=<optimized out>, m=m@entry=0x7ffff6570680 <QAbstractItemModel::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7fffffffd2f0) at kernel/qobject.cpp:3979
#7  0x00007ffff623d3ec in QAbstractItemModel::dataChanged(QModelIndex const&, QModelIndex const&, QVector<int> const&) (this=<optimized out>, _t1=<optimized out>, _t2=<optimized out>, _t3=<optimized out>)
    at .moc/moc_qabstractitemmodel.cpp:557
#8  0x00007ffff784625a in CollectionTreeItemModelBase::tracksLoaded(AmarokSharedPointer<Meta::Album> const&, QModelIndex const&, QList<AmarokSharedPointer<Meta::Track> > const&) () at /lib64/libamaroklib.so.1
#9  0x00007ffff62c8d40 in QObject::event(QEvent*) (this=0xaeda30, e=0x7fff9c002210) at kernel/qobject.cpp:1347
#10 0x00007ffff6f6240e in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=<optimized out>, receiver=0xaeda30, e=0x7fff9c002210) at kernel/qapplication.cpp:3637
#11 0x00007ffff629e888 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0xaeda30, event=0x7fff9c002210) at kernel/qcoreapplication.cpp:1064
#12 0x00007ffff62a15b9 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (receiver=0x0, event_type=0, data=0x446e30) at kernel/qcoreapplication.cpp:1821
#13 0x00007ffff62f3b03 in postEventSourceDispatch(GSource*, GSourceFunc, gpointer) (s=0x53f9f0) at kernel/qeventdispatcher_glib.cpp:277
#14 0x00007ffff1a4c689 in g_main_dispatch (context=0x7fffe4000ee0) at ../glib/gmain.c:3460
#15 g_main_context_dispatch (context=context@entry=0x7fffe4000ee0) at ../glib/gmain.c:4200
#16 0x00007ffff1a4ca18 in g_main_context_iterate (context=context@entry=0x7fffe4000ee0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4276
#17 0x00007ffff1a4ca9c in g_main_context_iteration (context=0x7fffe4000ee0, may_block=1) at ../glib/gmain.c:4343
#18 0x00007ffff62f31f6 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x54b220, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#19 0x00007ffff629d46b in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=this@entry=0x7fffffffd720, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#20 0x00007ffff62a4fe6 in QCoreApplication::exec() () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#21 0x00007ffff673034c in QGuiApplication::exec() () at kernel/qguiapplication.cpp:1870
#22 0x00007ffff6f62385 in QApplication::exec() () at kernel/qapplication.cpp:2829
#23 0x0000000000407fd7 in main(int, char**) (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/amarok-2.9.75-2.mga9.x86_64/src/main.cpp:389