未捕获的TypeError：无法读取属性＆＃39;朋友＆＃39;为null

Question

我有facebook multifriends选择器脚本，显示错误。

脚本：

window.fbAsyncInit = function () {

    //SDK loaded, initialize it

    var curLoc = window.location;

    FB.init({


        appId: 'xxxxxxxxxxxxx',

        xfbml: true,

        version: 'v2.0'

    });

    (function (d, s, id) {
        var js, fjs = d.getElementsByTagName(s)[0];
        if (d.getElementById(id)) {
            return;
        }
        js = d.createElement(s);
        js.id = id;
        js.src = "//connect.facebook.net/en_US/sdk.js";
        fjs.parentNode.insertBefore(js, fjs);
    }(document, 'script', 'facebook-jssdk'));


    FB.Canvas.setAutoGrow();
};

function renderMFS() {
    // First get the list of friends for this user with the Graph API
    FB.api('/me/friends', function (response) {
        var container = document.getElementById('mfs');
        var mfsForm = document.createElement('form');
        mfsForm.id = 'mfsForm';

        // Iterate through the array of friends object and create a checkbox for each   one.
        for (var i = 0; i < Math.min(response.data.length, 10); i++) {
            var friendItem = document.createElement('div');
            friendItem.id = 'friend_' + response.data[i].id;
            friendItem.innerHTML = '<input type="checkbox" name="friends" value="' + response.data[i].id + '" />' + response.data[i].name;
            mfsForm.appendChild(friendItem);
        }
        container.appendChild(mfsForm);

        // Create a button to send the Request(s)
        var sendButton = document.createElement('input');
        sendButton.type = 'button';
        sendButton.value = 'Send Request';
        sendButton.onclick = sendRequest;
        mfsForm.appendChild(sendButton);
    });
}

function sendRequest() {
    // Get the list of selected friends
    var sendUIDs = '';
    var mfsForm = document.getElementById('mfsForm');
    for (var i = 0; i < mfsForm.friends.length; i++) {
        if (mfsForm.friends[i].checked) {
            sendUIDs += mfsForm.friends[i].value + ',';
        }
    }

    // Use FB.ui to send the Request(s)
    FB.ui({
        method: 'apprequests',
        to: sendUIDs,
        title: 'My Great Invite',
        message: 'Check out this Awesome App!',
    }, callback);
}

function callback(response) {
    console.log(response);
}