Problem - no idea how to fix it -.-"

Error:

Undefined variable: checked in D:\Programs\XAMPP\htdocs\blog\admin\add-post.php on line 152

Here is code from line 130 - 155 so please help

130         <?php

            $stmt2 = $db->query('SELECT catID, catTitle FROM blog_cats ORDER BY catTitle');
            while($row2 = $stmt2->fetch()){

                if(isset($_POST['catID'])){

                    if(in_array($row2['catID'], $_POST['catID'])){
                       $checked="checked='checked'";
                    }else{
                       $checked = null;
                    }
                }

152             echo "<input type='checkbox' name='catID[]' value='".$row2['catID']."' $checked> ".$row2['catTitle']."<br />";
            }

155         ?>