code: public TrailingHeaders addHeader(CharSequence name, Iterable<Object> values) {
          lastHttpContent.trailingHeaders().add(name, values);
          return this;
      }
docs: Adds an HTTP trailing header with the passed {@code name} and {@code values} to this request.
  
  @param name Name of the header.
  @param values Values for the header.
  
  @return {@code this}.