anchor.diff:  
     @override
     void forEach(void f(String name, List<String> values)) {
  -    var forEachFunc = (name) {
  +    void forEachFunc(name) {
         var values = this[name];
         if (values != null && values.isNotEmpty) {
           f(name, values);
         }
  -    };
  +    }
   
       [
         HttpHeaders.ACCEPT_CHARSET,
  
positive.code:         if (!_request.hasBody) {
            return null;
          }
          return [contentLength];
        case HttpHeaders.CONTENT_TYPE:
          if (contentType == null) {
            return null;
  
negative.code: 
    @override
    void forEach(void f(String name, List<String> values)) => _headers.forEach(f);
    
    @override
    void clear() {
      _headers.clear();
    }
  
    @override
    void set host(String _host) {
  