jquery easyui combobox 添加一栏请选择

$('#department').combobox({
	    url:'data1.json', 
	    valueField:'value', textField:'text', required:true,
		editable:false, panelHeight:'auto', panelMaxHeight:200,
		label: '所属部门', labelPosition: 'left', width:250,
		loadFilter: function (data) {
			data.unshift({"value":'',"text":"请选择"});  return data;
		}
	});