title: Isset expression error
body: <p>I have basically coded a code which populates a list of categories from my database then you are able to select which to delete.</p>
  
  <p>I have the issue with the delete code which does not seem to work due to the error:</p>
  
  <pre><code>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
  </code></pre>
  
  <p>The line causing this is:</p>
  
  <pre><code>if(isset($_POST['delete_id'] &amp;&amp; !empty($_POST['delete_id']))) {
  </code></pre>
  
  <p>deletecategory.php</p>
  
  <pre><code>    &lt;h3&gt;
       Delete Category
      &lt;/h3&gt;
  
      &lt;?php $result = mysql_query("SELECT * FROM category"); ?&gt;
  
  &lt;table&gt;
    &lt;?php while($row = mysql_fetch_array($result)) : ?&gt;
    &lt;tr id="&lt;?php echo $row['category_id']; ?&gt;"&gt;
      &lt;td&gt;&lt;?php echo $row['category_Name']; ?&gt;&lt;/td&gt;
      &lt;td&gt;
        &lt;button class="del_btn" rel="&lt;?php echo $row['id']; ?&gt;"&gt;Delete&lt;/button&gt;
      &lt;/td&gt;
    &lt;/tr&gt;
    &lt;?php endwhile; ?&gt;
  &lt;/table&gt;
  
  &lt;script&gt;
    $(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!');
            }
         });
      });
    });
  &lt;/script&gt;
  </code></pre>
  
  <p>delete.php</p>
  
  <pre><code>&lt;?php
      if(isset($_POST['delete_id'] &amp;&amp; !empty($_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';
        }
      }
      ?&gt;
  </code></pre>