无法生成JQgrid-从控制器jquery错误返回json结果（ret == undefined）

Question

  

jquery错误ret == undefined。

我不明白这个错误是什么意思。呼叫转到控制器，并以json格式返回数据，但确切的错误是我没有得到它。

$(document).ready(function() {
    $('#Rohanclick').click(function () {
        debugger;
        jQuery("#searchGridStorage").jqGrid({
            url: "/Storage/Search",
            datatype: "json",
            colNames: ["Shipment ID", "Ship Date", "Ship To","Quantity"],
            colModel: [
                { name: "ShipmentID", index: "ShipmentID",
                  align: "center", width: 90 },
                { name: "ShipDate", index: "ShipDate", align: "center", 
                  width: 70 },
                { name: "ShipTo", index: "ShipTo", align: "center", 
                  width: 135 },
                { name: "Quantity", index: "Quantity", align: "center", 
                  width: 135 }
            ],
            mtype: "POST",
            //loadonce: true,
            rowNum: 10,
            page: 1,
            pager: $("#searchPager"),
            viewrecords: true,
            sortorder: "desc",
            caption: "List Details"
        });
        //$.Storage.LoadGrid(gridURL, "OSB");
    });