问如何获取空JQuery对象?

EN

//Init function.
$(function(){
//Hold the previously selected object for the account type selection.

var Previous = null;  //Here is where I would like to initialize.
                      //something like Previous = $();


$("SELECT[name='AccountType']").change(
    function () {
        //Hide Previous message if there was one.
        if(Previous == null || Previous.size() > 0){ 
            Previous.hide();
        }

        //Show the message if found and save it as previous.
        Previous = $("#"+this.value+"_Msg").show();

        //Get fisrt question
        var FirstQuestion = $(".FirstQuestion");
        if(this.value === ''){
            FirstQuestion.hide();
        }else{
            //Manually show FirstQuestion.
            FirstQuestion.show();
        }
    });
}

    var Previous = { size : function () { return 0; } };