CSS.escape('\0') should not throw.

third_party/WebKit/Source/core/css/CSSMarkup.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 182 matching lines @@
     appendTo.append(c);
 }
 
 static void serializeCharacterAsCodePoint(UChar32 c, StringBuilder& appendTo)
 {
     appendTo.append('\\');
     appendUnsignedAsHex(c, appendTo, Lowercase);
     appendTo.append(' ');
 }
 
-bool serializeIdentifier(const String& identifier, StringBuilder& appendTo)
+void serializeIdentifier(const String& identifier, StringBuilder& appendTo)
 {
     bool isFirst = true;
     bool isSecond = false;
     bool isFirstCharHyphen = false;
     unsigned index = 0;
     while (index < identifier.length()) {
         UChar32 c = identifier.characterStartingAt(index);
         if (c == 0) {
             // Check for lone surrogate which characterStartingAt does not return.
             c = identifier[index];
-            if (c == 0)
-                return false;
         }
 
         index += U16_LENGTH(c);
 
-        if (c <= 0x1f || c == 0x7f || (0x30 <= c && c <= 0x39 && (isFirst || (isSecond && isFirstCharHyphen))))
+        if (c == 0)
+            appendTo.append(0xfffd);
+        else if (c <= 0x1f || c == 0x7f || (0x30 <= c && c <= 0x39 && (isFirst || (isSecond && isFirstCharHyphen))))
             serializeCharacterAsCodePoint(c, appendTo);
         else if (c == 0x2d && isFirst && index == identifier.length())
             serializeCharacter(c, appendTo);
         else if (0x80 <= c || c == 0x2d || c == 0x5f || (0x30 <= c && c <= 0x39) || (0x41 <= c && c <= 0x5a) || (0x61 <= c && c <= 0x7a))
             appendTo.append(c);
         else
             serializeCharacter(c, appendTo);
 
         if (isFirst) {
             isFirst = false;
             isSecond = true;
             isFirstCharHyphen = (c == 0x2d);
         } else if (isSecond) {
             isSecond = false;
         }
     }
-    return true;
 }
 
 void serializeString(const String& string, StringBuilder& appendTo)
 {
     appendTo.append('\"');
 
     unsigned index = 0;
     while (index < string.length()) {
         UChar32 c = string.characterStartingAt(index);
         index += U16_LENGTH(c);
@@ skipping 14 matching lines @@
     serializeString(string, builder);
     return builder.toString();
 }
 
 String serializeURI(const String& string)
 {
     return "url(" + serializeString(string) + ")";
 }
 
 } // namespace blink