code: private static void addDateHeader(Request<?> request, String header, Date value) {
          if (value != null) {
              request.addHeader(header, ServiceUtils.formatRfc822Date(value));
          }
      }
docs: <p>
  Adds the specified date header in RFC 822 date format to the specified
  request.
  This method will not add a date header if the specified date value is <code>null</code>.
  </p>
  
  @param request
  The request to add the header to.
  @param header
  The header name.
  @param value
  The header value.