如何释放从CFStringTokenizerCreate创建的内存?

  CFStringTokenizerRef tokenRef = CFStringTokenizerCreate(NULL, 
                                   (CFStringRef)contents, 
                                   CFRangeMake(0, contents.length),
                                   kCFStringTokenizerUnitWordBoundary, 
                                   NULL);

  CFStringTokenizerTokenType tokenType;
  // leak reported here
  while ((tokenType = CFStringTokenizerAdvanceToNextToken(tokenRef)) != kCFStringTokenizerTokenNone) 

}

CFRelease(tokenRef);