Isset expression error

I have basically coded a code which populates a list of categories from my database then you are able to select which to delete. I have the issue with the delete code which does not seem to work due to the error: ``` Fatal error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead) in F:\xamppnew\htdocs\650032\admin\delete.php on line 6 ``` The line causing this is: ``` if(isset($_POST['delete_id'] && !empty($_POST['delete_id']))) { ``` deletecategory.php ``` <h3> Delete Category </h3> <?php $result = mysql_query("SELECT * FROM category"); ?> <table> <?php while($row = mysql_fetch_array($result)) : ?> <tr id="<?php echo $row['category_id']; ?>"> <td><?php echo $row['category_Name']; ?></td> <td> <button class="del_btn" rel="<?php echo $row['id']; ?>">Delete</button> </td> </tr> <?php endwhile; ?> </table> <script> $(document).ready(function(){ $('.del_btn').click(function(){ var del_id = $(this).attr('rel'); $.post('delete.php', {delete_id:del_id}, function(data) { if(data == 'true') { $('#'+del_id).remove(); } else { alert('Could not delete!'); } }); }); }); </script> ``` delete.php ``` <?php if(isset($_POST['delete_id'] && !empty($_POST['delete_id']))) { $delete_id = mysql_real_escape_string($_POST['delete_id']); $result = mysql_query("DELETE FROM category WHERE `id`=".$delete_id); if($result !== false) { echo 'true'; } } ?> ```