Check nullable value before using it in ReplaceSelectionCommand::removeRedundantStylesAndKeepStyleSp

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 500 matching lines @@
                 insertedNodes.willRemoveNodePreservingChildren(*element);
                 removeNodePreservingChildren(element);
                 continue;
             }
             removeNodeAttribute(element, styleAttr);
         } else if (newInlineStyle->style()->propertyCount() != inlineStyle->propertyCount()) {
             setNodeAttribute(element, styleAttr, AtomicString(newInlineStyle->style()->asText()));
         }
 
         // FIXME: Tolerate differences in id, class, and style attributes.
-        if (isNonTableCellHTMLBlockElement(element) && areIdenticalElements(element, element->parentNode())
+        if (element->parentNode() && isNonTableCellHTMLBlockElement(element) && areIdenticalElements(element, element->parentNode())
             && VisiblePosition(firstPositionInNode(element->parentNode())) == VisiblePosition(firstPositionInNode(element))
             && VisiblePosition(lastPositionInNode(element->parentNode())) == VisiblePosition(lastPositionInNode(element))) {
             insertedNodes.willRemoveNodePreservingChildren(*element);
             removeNodePreservingChildren(element);
             continue;
         }
 
         if (element->parentNode() && element->parentNode()->rendererIsRichlyEditable())
             removeNodeAttribute(element, contenteditableAttr);
 
@@ skipping 965 matching lines @@
         removeNodeAndPruneAncestors(nodeAfterInsertionPos.get());
 
     VisibleSelection selectionAfterReplace(m_selectReplacement ? start : end, end);
 
     setEndingSelection(selectionAfterReplace);
 
     return true;
 }
 
 } // namespace WebCore