lib/utils.js
function(callback){
			if(!this.id){
				return process.nextTick(function(){
					callback(new Error("Invalid session ID"));
				});
			}
			options.client.setex(options.keyspace + this.id, options.maxAge, JSON.stringify(serializeSession(this)), callback);
		}
function(callback){
			if(!this.id){
				return process.nextTick(function(){
					callback(new Error("Invalid session ID"));
				});
			}
			options.client.setex(options.keyspace + this.id, options.maxAge, JSON.stringify(serializeSession(this)), callback);
		}
function ( callback ) { if ( ! this . id ) { return process . nextTick ( function ( ) { callback ( new Error ( "Invalid session ID" ) ) ; } ) ; } options . client . setex ( options . keyspace + this . id , options . maxAge , JSON . stringify ( serializeSession ( this ) ) , callback ) ; }
update a session's data, update the ttl
update a session s data update the ttl