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