<ul>
    <li>アイテム1</li>
    <li>アイテム2</li>
    <li></li><!--空の要素-->
    <li>アイテム3</li>
</ul>
li {
    background-color: pink;
    padding: 5px;
    margin: 5px 0;
}
li:empty{/*空の要素を非表示にする*/
  display:none;
}
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