Ajax调用大小写未捕获的TypeError：

Question

我在核心2.1 mvc项目中有一个简单的ajax调用，当ajax被称为获取错误时。

Uncaught TypeError: Cannot read property 'toLowerCase' of undefined
    at jQuery.fn.init.val (jquery-3.3.1.js:7977)
    at Object.success (site.js?v=OUF1Fik5ylnQznBsXzwsHKsbqx7WPO22Vc7NQmDmM-c:268)
    at fire (jquery-3.3.1.js:3268)
    at Object.fireWith [as resolveWith] (jquery-3.3.1.js:3398)
    at done (jquery-3.3.1.js:9305)
    at XMLHttpRequest.<anonymous> (jquery-3.3.1.js:9548)
    at Object.send (jquery-3.3.1.js:9600)
    at Function.ajax (jquery-3.3.1.js:9206)
    at HTMLButtonElement.<anonymous> (site.js?v=OUF1Fik5ylnQznBsXzwsHKsbqx7WPO22Vc7NQmDmM-c:249)
    at HTMLDocument.dispatch (jquery-3.3.1.js:5183)
val @ jquery-3.3.1.js:7977
success @ site.js?v=OUF1Fik5ylnQznBsXzwsHKsbqx7WPO22Vc7NQmDmM-c:268
fire @ jquery-3.3.1.js:3268
fireWith @ jquery-3.3.1.js:3398
done @ jquery-3.3.1.js:9305
(anonymous) @ jquery-3.3.1.js:9548
send @ jquery-3.3.1.js:9600
ajax @ jquery-3.3.1.js:9206
(anonymous) @ site.js?v=OUF1Fik5ylnQznBsXzwsHKsbqx7WPO22Vc7NQmDmM-c:249
dispatch @ jquery-3.3.1.js:5183
elemData.handle @ jquery-3.3.1.js:4991
load (async)
send @ jquery-3.3.1.js:9567
ajax @ jquery-3.3.1.js:9206
(anonymous) @ site.js?v=OUF1Fik5ylnQznBsXzwsHKsbqx7WPO22Vc7NQmDmM-c:249
dispatch @ jquery-3.3.1.js:5183
elemData.handle @ jquery-3.3.1.js:4991

我只是通过传递一个变量来调用ajax来调用控制器，而html会刷新模式html

$.ajax({

        url: "/Home/CreateAddModalModel",
        type: "POST",
        async: false,
        data: {
            languageSelected: languageSelected

        },
        beforeSend: function () {

        },
        success: function (data) {


            $("#AddModalBody").html("");
            $("#AddModalBody").html(data);
            // Sync main dropdown with the one on the edit modal. Fire change event to reload transliterated rows
            $("#AddModalLanguagesDDLList")
                .val($(this).val())
                .trigger('change');

        },
        error: function (xhr, status, error) {

        }
    });
});