Changing the navigation for the root of a widget blueprint will cause a crash

 UE4Editor_UMGEditor!FWidgetNavigationCustomization::SetNav() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\umgeditor\private\customizations\widgetnavigationcustomization.cpp:244]
UE4Editor_UMGEditor!FWidgetNavigationCustomization::HandleNavMenuEntryClicked() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\editor\umgeditor\private\customizations\widgetnavigationcustomization.cpp:237]
UE4Editor_UMGEditor!TBaseSPMethodDelegateInstance<0,FWidgetNavigationCustomization,0,TTypeWrapper<void> __cdecl(void),TWeakPtr<IPropertyHandle,0>,enum EUINavigation,enum EUINavigationRule>::Execute() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:282]
UE4Editor_UMGEditor!TBaseSPMethodDelegateInstance<0,FWidgetNavigationCustomization,0,void __cdecl(void),TWeakPtr<IPropertyHandle,0>,enum EUINavigation,enum EUINavigationRule>::ExecuteIfSafe() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:388]
UE4Editor_Slate!SMenuEntryBlock::OnClicked() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\multibox\smenuentryblock.cpp:988]
UE4Editor_Slate!SMenuEntryBlock::OnMenuItemButtonClicked() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\multibox\smenuentryblock.cpp:939]
UE4Editor_Slate!TMemberFunctionCaller<SMenuEntryBlock,FReply (__cdecl SMenuEntryBlock::*)(void) __ptr64>::operator()<>() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\public\delegates\delegateinstanceinterface_variadics.h:161]
UE4Editor_Slate!TTupleImpl<TIntegerSequence<> >::ApplyAfter_ExplicitReturnType<FReply,TMemberFunctionCaller<SMenuEntryBlock,FReply (__cdecl SMenuEntryBlock::*)(void) __ptr64> >() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\public\delegates\tuple.h:113]
UE4Editor_Slate!TBaseSPMethodDelegateInstance<0,SMenuEntryBlock,0,FReply __cdecl(void)>::Execute() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:282]
UE4Editor_Slate!TBaseDelegate<FReply>::Execute() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\public\delegates\delegatesignatureimpl_variadics.inl:440]
UE4Editor_Slate!SButton::OnMouseButtonUp() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:236]
UE4Editor_Slate!SMenuEntryButton::OnMouseButtonUp() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\multibox\smenuentryblock.cpp:361]
UE4Editor_Slate!<lambda_df946b2745ea2bbab398d4acc9cc3d04>::operator()() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4273]
UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FToLeafmostPolicy,FPointerEvent,<lambda_df946b2745ea2bbab398d4acc9cc3d04> >() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:214]
UE4Editor_Slate!FSlateApplication::RoutePointerUpEvent() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4276]
UE4Editor_Slate!FSlateApplication::ProcessMouseButtonUpEvent() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4660]
UE4Editor_Slate!FSlateApplication::OnMouseUp() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4638]
UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\private\windows\windowsapplication.cpp:1403]
UE4Editor_Core!FWindowsApplication::DeferMessage() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\private\windows\windowsapplication.cpp:1708]
UE4Editor_Core!FWindowsApplication::ProcessMessage() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\private\windows\windowsapplication.cpp:706]
UE4Editor_Core!FWindowsApplication::AppWndProc() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\private\windows\windowsapplication.cpp:628]
user32
user32
UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:884]
UE4Editor!FEngineLoop::Tick() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\launchengineloop.cpp:2392]
UE4Editor!GuardedMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\launch.cpp:142]
UE4Editor!GuardedMainWrapper() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() [d:\buildfarm\buildmachine_++depot+ue4-releases+4.9\engine\source\runtime\launch\private\windows\launchwindows.cpp:200]