Don't return null from ReplaceSelectionCommand::insertAsListItems()

Source/core/editing/ReplaceSelectionCommand.cpp

 /*
  * Copyright (C) 2005, 2006, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009, 2010, 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 1429 matching lines @@
         if (isStart || isMiddle) {
             insertNodeBefore(listItem, lastNode);
             insertedNodes.respondToNodeInsertion(*listItem);
         } else if (isEnd) {
             insertNodeAfter(listItem, lastNode);
             insertedNodes.respondToNodeInsertion(*listItem);
             lastNode = listItem.get();
         } else
             ASSERT_NOT_REACHED();
     }
-    if (isStart || isMiddle)
-        lastNode = lastNode->previousSibling();
+    if (isStart || isMiddle) {
+        if (Node* node = lastNode->previousSibling())
+            return node;
+    }
     return lastNode;
 }
 
 void ReplaceSelectionCommand::updateNodesInserted(Node *node)
 {
     if (!node)
         return;
 
     if (m_startOfInsertedContent.isNull())
         m_startOfInsertedContent = firstPositionInOrBeforeNode(node);
@@ skipping 32 matching lines @@
         removeNodeAndPruneAncestors(nodeAfterInsertionPos.get());
 
     VisibleSelection selectionAfterReplace(m_selectReplacement ? start : end, end);
 
     setEndingSelection(selectionAfterReplace);
 
     return true;
 }
 
 } // namespace WebCore