anchor.diff:        } else {
           throw new HttpException("Unexpected type for header named $name");
         }
  -    } else if (name.toLowerCase() == "if-modified-since") {
  +    } else if (lowerCaseName == "if-modified-since") {
         if (value is Date) {
           ifModifiedSince = value;
         } else if (value is String) {
  
positive.code:       } else {
          throw new HttpException("Unexpected type for header named $name");
        }
      } else if (name.toLowerCase() == "host") {
        int pos = value.indexOf(":");
        if (pos == -1) {
          _host = value;
  
negative.code:   }
  
    void _add(String name, Object value) {
      var lowerCaseName = name.toLowerCase();
      // TODO(sgjesse): Add immutable state throw HttpException is immutable.
      if (lowerCaseName == "date") {
        if (value is Date) {
          date = value;
        } else if (value is String) {
  