code: @Override
      public void setTrailerFields(Supplier<Map<String, String>> supplier) {
          _getHttpServletResponse().setTrailerFields(supplier);
      }
docs: The default behaviour of this method is to call
  {@link HttpServletResponse#setTrailerFields} on the wrapped response
  object.
  
  @param supplier of trailer headers
  
  @since Servlet 4.0