From c87f3d5918db8956f2d8f4bcf13dcd896ef82d28 Mon Sep 17 00:00:00 2001
From: roytam1 <roytam@gmail.com>
Date: Wed, 3 Mar 2021 10:12:43 +0800
Subject: [PATCH] partly imported Bug 1183896. Don't assume that relatively
 positioned table cells actually have positioned offsets computed, because in
 the case of position:sticky they don't. r=dholbert

---
 layout/tables/nsTableRowFrame.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/layout/tables/nsTableRowFrame.cpp b/layout/tables/nsTableRowFrame.cpp
index 5516caa0fc..bda622ef1a 100644
--- a/layout/tables/nsTableRowFrame.cpp
+++ b/layout/tables/nsTableRowFrame.cpp
@@ -991,8 +991,12 @@ nsTableRowFrame::ReflowChildren(nsPresContext*           aPresContext,
         // We didn't reflow.  Do the positioning part of what
         // MovePositionBy does internally.  (This codepath should really
         // be merged into the else below if we can.)
-        LogicalMargin computedOffsets(wm, *static_cast<nsMargin*>
-          (kidFrame->Properties().Get(nsIFrame::ComputedOffsetProperty())));
+        nsMargin* computedOffsetProp = static_cast<nsMargin*>
+          (kidFrame->Properties().Get(nsIFrame::ComputedOffsetProperty()));
+        // Bug 975644: a position:sticky kid can end up with a null
+        // property value here.
+        LogicalMargin computedOffsets(wm, computedOffsetProp ?
+                                            *computedOffsetProp : nsMargin());
         nsHTMLReflowState::ApplyRelativePositioning(kidFrame, wm, computedOffsets,
                                                     &kidPosition, containerWidth);
       }