Handle null baseStyle in getPropertiesNotIn

Source/core/editing/EditingStyle.cpp

 /*
  * Copyright (C) 2007, 2008, 2009 Apple Computer, Inc.
  * Copyright (C) 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 1407 matching lines @@
 
 StyleChange::StyleChange(EditingStyle* style, const Position& position)
     : m_applyBold(false)
     , m_applyItalic(false)
     , m_applyUnderline(false)
     , m_applyLineThrough(false)
     , m_applySubscript(false)
     , m_applySuperscript(false)
 {
     Document* document = position.document();
-    if (!style || !style->style() || !document || !document->frame())
+    if (!style || !style->style() || !document || !document->frame() || !position.element())
         return;
 
     RefPtrWillBeRawPtr<CSSComputedStyleDeclaration> computedStyle = position.computedStyle();
     // FIXME: take care of background-color in effect
     RefPtrWillBeRawPtr<MutableStylePropertySet> mutableStyle = getPropertiesNotIn(style->style(), computedStyle.get());
+    ASSERT(mutableStyle);
 
     reconcileTextDecorationProperties(mutableStyle.get());
     if (!document->frame()->editor().shouldStyleWithCSS())
         extractTextStyles(document, mutableStyle.get(), computedStyle->fixedPitchFontType());
 
     // Changing the whitespace style in a tab span would collapse the tab into a space.
     if (isTabHTMLSpanElementTextNode(position.deprecatedNode()) || isTabHTMLSpanElement((position.deprecatedNode())))
         mutableStyle->removeProperty(CSSPropertyWhiteSpace);
 
     // If unicode-bidi is present in mutableStyle and direction is not, then add direction to mutableStyle.
@@ skipping 234 matching lines @@
 {
     for (Node* ancestor = node; ancestor; ancestor = ancestor->parentNode()) {
         RefPtrWillBeRawPtr<CSSComputedStyleDeclaration> ancestorStyle = CSSComputedStyleDeclaration::create(ancestor);
         if (!hasTransparentBackgroundColor(ancestorStyle.get()))
             return ancestorStyle->getPropertyCSSValue(CSSPropertyBackgroundColor);
     }
     return nullptr;
 }
 
 }