code: @Override
      public Map<String, List<String>> headers() {
          if (headers != null) {
              return headers;
          }
          headers = new HashMap<>();
          final MultiMap requestHeaders = request.headers();
          Set<String> names = requestHeaders.names();
          for (String name : names) {
              headers.put(name, requestHeaders.getAll(name));
          }
          return headers;
      }
docs: Retrieves all headers.
  
  @return headers