walker disappears

I have a walker main menu that works great and its a sticky menu as well, but when I customised the comment form the sticky menu still worked but it disappeared. What I mean is all the height of the menu and the border bottom was still there but couldn’t see the menu. This is the code I used to customise the comments.

$args = array(

                    'walker'             =>  null,
                    'max_depth'          =>  '',
                    'style'              =>  'ol',
                    'callback'           =>  null,
                    'end-callback'       =>  null,
                    'type'               =>  'all',
                    'reply_text'         =>  'reply',
                    'page'               =>  '',
                    'per_page'           =>  '',
                    'avatar_size'        =>  64,
                    'reverse_top_level'  => null,
                    'reverse_children'   => '',
                    'format'             => 'html5',
                    'short_ping'         => false,
                    'echo'               => true

                );

                wp_list_comments( $args );

Even if I take the walker out of the $args its still not visible when fixed.