CrashTracer: MobileSafari at WebKit: -[WKWebView(WKViewInternalIOS) _…

…updateScrollViewForTransaction:]

https://bugs.webkit.org/show_bug.cgi?id=241563
<rdar://94621991>

Reviewed by Wenson Hsieh.

Protect against a null root scrolling node.

* Source/WebKit/UIProcess/API/ios/WKWebViewIOS.mm:
(-[WKWebView _updateScrollViewForTransaction:]):

Canonical link: https://commits.webkit.org/251509@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@295504 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebKit/UIProcess/API/ios/WKWebViewIOS.mm

@@ -876,8 +876,16 @@ - (void)_updateScrollViewForTransaction:(const WebKit::RemoteLayerTreeTransactio
     [_scrollView setMinimumZoomScale:layerTreeTransaction.minimumScaleFactor()];
     [_scrollView setMaximumZoomScale:layerTreeTransaction.maximumScaleFactor()];
     [_scrollView _setZoomEnabledInternal:layerTreeTransaction.allowsUserScaling()];
-    auto rootNode = _page->scrollingCoordinatorProxy()->rootNode();
-    WebKit::ScrollingTreeScrollingNodeDelegateIOS::updateScrollViewForOverscrollBehavior(_scrollView.get(), rootNode->horizontalOverscrollBehavior(), rootNode->verticalOverscrollBehavior(), WebKit::ScrollingTreeScrollingNodeDelegateIOS::AllowOverscrollToPreventScrollPropagation::No);
+
+    auto horizontalOverscrollBehavior = WebCore::OverscrollBehavior::Auto;
+    auto verticalOverscrollBehavior = WebCore::OverscrollBehavior::Auto;
+
+    if (auto rootNode = _page->scrollingCoordinatorProxy()->rootNode()) {
+        horizontalOverscrollBehavior = rootNode->horizontalOverscrollBehavior();
+        verticalOverscrollBehavior = rootNode->verticalOverscrollBehavior();
+    }
+
+    WebKit::ScrollingTreeScrollingNodeDelegateIOS::updateScrollViewForOverscrollBehavior(_scrollView.get(), horizontalOverscrollBehavior, verticalOverscrollBehavior, WebKit::ScrollingTreeScrollingNodeDelegateIOS::AllowOverscrollToPreventScrollPropagation::No);
 
     bool hasDockedInputView = !CGRectIsEmpty(_inputViewBoundsInWindow);
     bool isZoomed = layerTreeTransaction.pageScaleFactor() > layerTreeTransaction.initialScaleFactor();