How to disable validation on dijit.form.FilteringSelect?

http://stackoverflow.com/questions/14333145/how-to-disable-validation-on-dijit-form-filteringselect

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.8.1/dijit/themes/claro/claro.css">
<div id="stateSelect"></div>
<input dojoType="dijit.form.FilteringSelect" id="contratto" name="contratto" style="width:200px;" required="false" pageSize="15" queryExpr="*${0}*" autoComplete="false"/>

JavaScript

contratto= [
            {name:"Alabama", id:"AL"},
            {name:"Alaska", id:"AK"},
            {name:"American Samoa", id:"AS"},
            {name:"Arizona", id:"AZ"},
            {name:"Arkansas", id:"AR"},
            {name:"Armed Forces Europe", id:"AE"},
            {name:"Armed Forces Pacific", id:"AP"},
            {name:"Armed Forces the Americas", id:"AA"},
            {name:"California", id:"CA"},
            {name:"Colorado", id:"CO"},
            {name:"Connecticut", id:"CT"},
            {name:"Delaware", id:"DE"}
        ];
        
        dijit.byId("contratto").store=new dojo.data.ItemFileReadStore({ data: dojo.fromJson(contratto) });