I somehow made a WPE build that triggers this crash, where the quirksUserAgentStyleSheet string is null... (gdb) bt #0 0x00007fa2a3141589 in WTF::StringView::StringView(WTF::StringImpl const*) (string=0x0, this=<optimized out>) at WTF/Headers/wtf/text/StringConcatenate.h:430 #1 WTF::StringTypeAdapter<WTF::StringImpl*, void>::writeTo<unsigned char>(unsigned char*) const (destination=0x7fa2940e84b0 "", this=<optimized out>) at WTF/Headers/wtf/text/StringConcatenate.h:188 #2 WTF::stringTypeAdapterAccumulator<unsigned char, WTF::StringTypeAdapter<WTF::String, void> >(unsigned char*, WTF::StringTypeAdapter<WTF::String, void>) (result=0x7fa2940e84b0 "", adapter=...) at WTF/Headers/wtf/text/StringConcatenate.h:423 #3 WTF::stringTypeAdapterAccumulator<unsigned char, WTF::StringTypeAdapter<WTF::String, void>, WTF::StringTypeAdapter<WTF::String, void> >(unsigned char*, WTF::StringTypeAdapter<WTF::String, void>, WTF::StringTypeAdapter<WTF::String, void>) (result=<optimized out>, adapter=..., adapters=...) at WTF/Headers/wtf/text/StringConcatenate.h:430 #4 WTF::tryMakeStringImplFromAdaptersInternal<WTF::StringTypeAdapter<WTF::String, void>, WTF::StringTypeAdapter<WTF::String, void> >(unsigned int, bool, WTF::StringTypeAdapter<WTF::String, void>, WTF::StringTypeAdapter<WTF::String, void>) (length=348, areAllAdapters8Bit=<optimized out>, adapter=..., adapters=...) at WTF/Headers/wtf/text/StringConcatenate.h:444 #5 0x00007fa2a33f90bd in WTF::tryMakeStringFromAdapters<WTF::StringTypeAdapter<WTF::String, void>, WTF::StringTypeAdapter<WTF::String, void> >(WTF::StringTypeAdapter<WTF::String, void>, WTF::StringTypeAdapter<WTF::String, void>) (adapter=..., adapters=...) at WTF/Headers/wtf/text/StringConcatenate.h:475 #6 WTF::tryMakeString<WTF::String, WTF::String>(WTF::String, WTF::String) (strings=..., strings=...) at WTF/Headers/wtf/text/StringConcatenate.h:481 #7 WTF::StringAppend<WTF::String, WTF::String>::operator WTF::String() const (this=0x7fff176fe608) at WTF/Headers/wtf/text/StringOperators.h:38 #8 0x00007fa2a5dc046c in WebCore::Style::UserAgentStyle::initDefaultStyleSheet() () at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/style/UserAgentStyle.cpp:158 #9 0x00007fa2a5da6460 in WebCore::Style::Resolver::Resolver(WebCore::Document&) (this=0x7fa0aa000a80, document=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/style/StyleResolver.cpp:147 #10 0x00007fa2a5daabfb in WebCore::Style::Resolver::create(WebCore::Document&) (document=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/style/StyleResolver.cpp:139 #11 WebCore::Style::Scope::createDocumentResolver() (this=0x7fa2940c4400) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/style/StyleScope.cpp:104 #12 0x00007fa2a5daa5be in WebCore::Style::Scope::resolver() (this=0x7fa2940c4400) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/style/StyleScope.cpp:89 #13 0x00007fa2a5dbd310 in WebCore::Style::TreeResolver::resolve() (this=0x7fff176fe818) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/style/StyleTreeResolver.cpp:909 #14 0x00007fa2a529a6ad in WebCore::Document::resolveStyle(WebCore::Document::ResolveStyleType) (this=0x7fa2420e0000, type=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/dom/Document.cpp:2091 #15 0x00007fa2a529bc61 in WebCore::Document::createRenderTree() (this=0x7fa2420e0000) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/dom/Document.cpp:2501 #16 0x00007fa2a529bcfe in WebCore::Document::didBecomeCurrentDocumentInFrame() (this=0x7fa2420e0000) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/dom/Document.cpp:2513 #17 0x00007fa2a58077c2 in WebCore::Frame::setDocument(WTF::RefPtr<WebCore::Document, WTF::RawPtrTraits<WebCore::Document>, WTF::DefaultRefDerefTraits<WebCore::Document> >&&) (this=0x7fa2940a0f00, newDocument=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/page/Frame.cpp:313 #18 0x00007fa2a57084a1 in WebCore::DocumentWriter::begin(WTF::URL const&, bool, WebCore::Document*, WebCore::ProcessQualified<WTF::UUID>) (this=0x7fa24201d060, urlReference=..., dispatch=false, ownerDocument=0x0, documentIdentifier=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/loader/DocumentWriter.cpp:180 #19 0x00007fa2a57030cc in WebCore::DocumentLoader::commitData(WebCore::SharedBuffer const&) (this=0x7fa24201d000, data=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/loader/DocumentLoader.cpp:1235 #20 0x00007fa2a5702a5c in WebCore::DocumentLoader::finishedLoading() (this=0x7fa24201d000) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/loader/DocumentLoader.cpp:493 #21 0x00007fa2a570ad07 in WebCore::DocumentLoader::maybeLoadEmpty() (this=0x7fa24201d000) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/loader/DocumentLoader.cpp:2043 #22 0x00007fa2a570afe4 in WebCore::DocumentLoader::startLoadingMainResource() (this=0x7fa24201d000) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/loader/DocumentLoader.cpp:2070 #23 0x00007fa2a5722e92 in WebCore::FrameLoader::init() (this=0x7fa294028340) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebCore/loader/FrameLoader.cpp:351 #24 0x00007fa2a33e6812 in WebKit::WebFrame::initWithCoreMainFrame(WebKit::WebPage&, WebCore::Frame&) (this=0x7fa294004480, page=<optimized out>, coreFrame=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/WebProcess/WebPage/WebFrame.cpp:115 #25 0x00007fa2a33c27b7 in WebKit::WebPage::WebPage(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&) (this=0x7fa2940e4100, pageID=..., parameters=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/WebProcess/WebPage/WebPage.cpp:725 #26 0x00007fa2a33c12b3 in WebKit::WebPage::create(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&) (pageID=..., parameters=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/WebProcess/WebPage/WebPage.cpp:465 #27 0x00007fa2a32fffd5 in WebKit::WebProcess::createWebPage(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&) (this=0x7fa294030210, pageID=..., parameters=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/WebProcess/WebProcess.cpp:837 #28 0x00007fa2a2eed2d1 in IPC::callMemberFunctionImpl<WebKit::WebProcess, void (WebKit::WebProcess::*)(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&), std::tuple<WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters>, 0ul, 1ul>(WebKit::WebProcess*, void (WebKit::WebProcess::*)(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&), std::tuple<WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters>&&, std::integer_sequence<unsigned long, 0ul, 1ul>) (object=0x7fa294030210, function=<optimized out>, args=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Platform/IPC/HandleMessage.h:131 #29 IPC::callMemberFunction<WebKit::WebProcess, void (WebKit::WebProcess::*)(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&), std::tuple<WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters>, std::integer_sequence<unsigned long, 0ul, 1ul> >(std::tuple<WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters>&&, WebKit::WebProcess*, void (WebKit::WebProcess::*)(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&)) (args=..., object=0x7fa294030210, function=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Platform/IPC/HandleMessage.h:137 #30 IPC::handleMessage<Messages::WebProcess::CreateWebPage, WebKit::WebProcess, void (WebKit::WebProcess::*)(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&)>(IPC::Connection&, IPC::Decoder&, WebKit::WebProcess*, void (WebKit::WebProcess::*)(WTF::ObjectIdentifier<WebCore::PageIdentifierType>, WebKit::WebPageCreationParameters&&)) (connection=<optimized out>, decoder=..., object=0x7fa294030210, function=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Platform/IPC/HandleMessage.h:259 #31 WebKit::WebProcess::didReceiveWebProcessMessage(IPC::Connection&, IPC::Decoder&) (this=0x7fa294030210, connection=<optimized out>, decoder=...) at DerivedSources/WebKit/WebProcessMessageReceiver.cpp:280 #32 0x00007fa2a30c462e in IPC::Connection::dispatchMessage(IPC::Decoder&) (this=0x7fa2940501a0, decoder=...) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Platform/IPC/Connection.cpp:1105 #33 0x00007fa2a30c4913 in IPC::Connection::dispatchMessage(std::unique_ptr<IPC::Decoder, std::default_delete<IPC::Decoder> >) (this=0x7fa2940501a0, message=std::unique_ptr<IPC::Decoder> = {...}) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Platform/IPC/Connection.cpp:1150 #34 0x00007fa2a30c4c3e in IPC::Connection::dispatchOneIncomingMessage() (this=0x7fa2940501a0) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Platform/IPC/Connection.cpp:1219 #35 0x00007fa2a4449ccd in WTF::Function<void ()>::operator()() const (this=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/Function.h:82 #36 WTF::RunLoop::performWork() (this=0x7fa2940100e0) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/RunLoop.cpp:133 #37 0x00007fa2a44a7f8d in WTF::RunLoop::RunLoop()::$_1::operator()(void*) const (userData=0x7fa2940e8460, userData@entry=0x7fa2940100e0, this=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/glib/RunLoopGLib.cpp:80 #38 WTF::RunLoop::RunLoop()::$_1::__invoke(void*) (userData=0x7fa2940e8460) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/glib/RunLoopGLib.cpp:79 #39 0x00007fa2a44a739e in WTF::RunLoop::$_0::operator()(_GSource*, int (*)(void*), void*) const (source=0x11df990, callback=0x7fa2a44a7f80 <WTF::RunLoop::RunLoop()::$_1::__invoke(void*)>, userData=0x7fa2940100e0, this=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/glib/RunLoopGLib.cpp:53 #40 WTF::RunLoop::$_0::__invoke(_GSource*, int (*)(void*), void*) (source=0x11df990, callback=0x7fa2a44a7f80 <WTF::RunLoop::RunLoop()::$_1::__invoke(void*)>, userData=0x7fa2940100e0) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/glib/RunLoopGLib.cpp:45 #41 0x00007fa2a2088faf in g_main_context_dispatch () at /lib64/libglib-2.0.so.0 #42 0x00007fa2a20de2c8 in g_main_context_iterate.constprop () at /lib64/libglib-2.0.so.0 #43 0x00007fa2a20886cf in g_main_loop_run () at /lib64/libglib-2.0.so.0 #44 0x00007fa2a44a7983 in WTF::RunLoop::run() () at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WTF/wtf/glib/RunLoopGLib.cpp:108 #45 0x00007fa2a33ff1f1 in WebKit::AuxiliaryProcessMainBase<WebKit::WebProcess, true>::run(int, char**) (this=0x7fff176ffee0, argc=3, argv=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Shared/AuxiliaryProcessMain.h:71 #46 WebKit::AuxiliaryProcessMain<WebKit::WebProcessMainWPE>(int, char**) (argc=3, argv=<optimized out>) at /usr/src/debug/wpewebkit-2.38.0-1.fc36.x86_64/Source/WebKit/Shared/AuxiliaryProcessMain.h:97 #47 0x00007fa2a24b0550 in __libc_start_call_main () at /lib64/libc.so.6 #48 0x00007fa2a24b0609 in __libc_start_main_impl () at /lib64/libc.so.6 #49 0x0000000000401075 in _start ()