Merge 78168 - 2011-02-09 Ryosuke Niwa <rniwa@webkit.org>...

Source/WebCore/editing/VisibleSelection.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Apple Computer, 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 155 matching lines @@
         if (comparePositions(s, e) > 0) {
             // Make sure the start is before the end.
             // The end can wind up before the start if collapsed whitespace is the only thing selected.
             Position tmp = s;
             s = e;
             e = tmp;
         }
         s = s.parentAnchoredEquivalent();
         e = e.parentAnchoredEquivalent();
     }
+    
+    if (s.isNull() || e.isNull())
+        return 0;
 
     // VisibleSelections are supposed to always be valid.  This constructor will ASSERT
     // if a valid range could not be created, which is fine for this callsite.
     return Range::create(s.node()->document(), s, e);
 }
 
 bool VisibleSelection::expandUsingGranularity(TextGranularity granularity)
 {
     if (isNone())
         return false;
@@ skipping 452 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const WebCore::VisibleSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif