拖拽插件报错Sortable报错Sortable: `el` must be HTMLElement, and not [object Null]

之前还好好的，代码也没有一点改动
然后就报错
Uncaught Sortable: el must be HTMLElement, and not [object Null]

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script src="Sortable.js"></script>
        <script src="jquery.js"></script>
        <style>
            .sotr {
                width: 500px;
                height: 300px;
                margin: 100px auto 10px;
                border: 1px solid #ddd;
            }

            .sotr a {
                float: left;
                display: block;
                width: 100px;
                height: 100px;
                margin: 10px;
            }

            .click {
                width: 100px;
                height: 100px;
                background: #DDDDDD;
                margin: 0 auto;
                text-align: center;
            }

            .upset {
                width: 100px;
                height: 100px;
                background: #DDDDDD;
                margin: 0px auto;
                text-align: center;
            }
        </style>


    </head>
    <body>
        <div id="sotr" class="sotr">
            <a data-index='0' style="background: #aa0000;">1</a>
            <a data-index='1' style="background: #005500;">2</a>
            <a data-index='2' style="background: #aa5500;">3</a>
            <a data-index='3' style="background: #59d57f;">4</a>
            <a data-index='4' style="background: #00ffff;">5</a>
            <a data-index='5' style="background: #ff007f;">6</a>
            <a data-index='6' style="background: #ffff7f;">7</a>
            <a data-index='7' style="background: #5500ff;">8</a>
        </div>
        <div id="click" class="click">提交</div>
        <div id="upset" class="upset">打乱</div>
    </body>
    <script>
            window.onload = function () {
                /////////初始滑动插件
                var foo = document.getElementById("#sotr");
                Sortable.create(foo, {
                    group: "adva"
                });
     
       
                function shffle() {
                    let array = $('#sotr a')
                    let usedIndex = []
                    let newArray = []
                    let validCount = []
     
                    top:
                    while (validCount < array.length) {
                        let index = Math.floor(Math.random() * array.length)
                        if (usedIndex.indexOf(index) > -1) {
                            continue top
                        } else {
                            usedIndex.push(index)
                        }
                        validCount++
                        newArray.push(array[index])
                    }
                    let newarr = shuffle()
                    for (let item of newarr) {
                        $('#sotr').append(item)
                    }
                }
                $('#upset').on('click', shffle)
          
     }
        </script>



</html>

刚开始还是能把DIV顺序打乱

现在没效果了

这个 js 贴出来

出错位置


function Sortable(el, options) {
        if (!(el && el.nodeType && el.nodeType === 1)) {
            throw 'Sortable: `el` must be HTMLElement, and not ' + {}.toString.call(el);
        }