code: private Date lastModified() {
  		Date clientDate = currentRequest().clientDate();
  		Date lastModified=new Date();
  		if(clientDate!=null && clientDate.after(lastModified)) {
  			lastModified=clientDate;
  		}
  		return lastModified;
  	}
docs: Enforce http://tools.ietf.org/html/rfc7232#section-2.2:
  if the clock in the request is ahead of the clock of the origin
  server (e.g., I request from Spain the update of a resource held in USA)
  the last-modified data should be changed to that of the request and not
  a generated date from the origin server