Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, boolean given in

<?php
                $article = mysqli_query($connection, "SELECT * FROM  `article` WHERE `id` = ".(int) $_GET['id']);
            ?>
            <?php
                $art = mysqli_fetch_assoc($article);
                  {
            ?>

    <?php 
        $comments = mysqli_query($connection, "SELECT * FROM `comments` WHERE `article_id` = " .(int) $art['id']. "ORDER BY `id` DESC");
    if(mysqli_num_rows($comments) <=0)
    {
     echo "Нет коментариев";
    }
    while ($comment = mysqli_fetch_assoc($comments))
    {
    ?>
    <article class="article">
        <div class="article_image" style="background-image: url(https://www.gravatar.com/avatar/<?php echo md5($comment['email']); ?>?s=125);"></div>
        <div class="article_info">
            <a href="/article.php?id=<?php echo $comment['article_id']; ?>"><?php echo $comment['author_comment']; ?> </a>
                <div class="article_info_meta"></div>
                <div class="article_info_peview"><?php echo mb_substr(strip_tags($comment['text']), 0, 100,'utf-8'). '...'; ?> </div>
                </div>
                </article>
                <?php
    }
    ?>

.(int)htmlspecialchars($_GET[$art['id']]).

if(mysqli_num_rows($comments) <=0)
    {
     echo "Нет комментариев";
    }

    while ($comment = mysqli_fetch_assoc($comments))
    {
    ?>
    <article class="article">
        <div class="article_image" style="background-image: url(https://www.gravatar.com/avatar/<?php echo md5($comment['email']); ?>?s=125);"></div>
        <div class="article_info">
            <a href="/article.php?id=<?php echo $comment['article_id']; ?>"><?php echo $comment['author_comment']; ?> </a>
                <div class="article_info_meta"></div>
                <div class="article_info_peview"><?php echo mb_substr(strip_tags($comment['text']), 0, 100,'utf-8'). '...'; ?> </div>
                </div>
                </article>
                <?php
    }