comment_reply_link WordPress function not working for me

I design my own comment lay out using

<?php

if (post_password_required())
return;
?>
<div class="left">
<?php
global $post;
$number_of_comments = wp_count_comments($post->ID);
comments_number('0 Replies', 'One Reply', "$number_of_comments->approved Replies");
?>  
</div>
<?php
$sfp_reply = get_comments("post_id=$post->ID");
if ($sfp_reply) :
?>  

<?php
foreach ($sfp_reply as $comment)
{
    $comment_user = get_userdata($comment->user_id);
    ?>

    <section class='post-thread' id="comment-<?php comment_ID(); ?>">
        <div class="thread-post-detail">
            <div class="thread-user-pic">
                <?php
                echo "<img class='img-responsive' src='" . get_picture($comment->comment_author, 75) . "' />"
                ?>
            </div>
            <div class="thread-user-info">
                <a href="<?php echo site_url() . "/author/" . $comment_user->user_login ?>">
                    <div class='thread_user_name'><strong><?php echo ucfirst($comment_user->first_name); ?></strong></div>
                    <div class='thread_user_name'><strong><?php echo ucfirst($comment_user->last_name); ?></strong></div>
                </a>
                <div class="user-join-date">Joined <?php
                    $join_date_time = $comment_user->user_registered;
                    $join_date = new DateTime($join_date_time);

                    echo $join_date = $join_date->format('m.d.y');
                    ?>
                </div>
                <div class="sfpuserreply">
                    <div class="sfpicon-text left fblikelogo">Likes</div>
                    <div class="user-social-count left "><?php
                        if ($userlikes = get_user_meta($comment_user->ID, 'sfp_user_like_count'))
                            echo $userlikes[0];
                        else
                            echo 0;
                        ?>
                    </div>
                </div>
                <div class="sfpuserreply">
                    <div class="sfpicon-text left fbsharelogo">Share</div>
                    <div class="user-social-count left">
                        <?php
                        if ($usershare = get_user_meta($comment_user->ID, 'sfp_user_fb_share'))
                            echo $usershare[0];
                        else
                            echo 0;
                        ?>
                    </div>
                </div>
                <div class="sfpuserreply">
                    <div class="sfpicon-text left">Replies</div>
                    <div class="user-social-count left"><?php $comments = get_comments('user_id=' . $comment_user->ID);
                    echo count($comments); ?></div>
                </div>
            </div>
        </div>
        <div class="thread-post-content">
            <div class="thread-posted">Posted 
            <?php
            $post_time_date = $comment->comment_date;
            $post_time_date = new DateTime($post_time_date);
            echo $post_time_date->format('d.m.Y') . " @ " . $post_time_date->format('H:i A');
            ?>
            </div>
    <?php if ($comment->comment_approved == '0') : ?>  
                <p>Your comment is awaiting approval</p>  
    <?php endif; ?> 
                <div class="thread_single_content"><?php echo nl2br($comment->comment_content); ?></div>
        </div>
        <div class="comment-reply-data">
            <?php
//                var_dump($comment);
            var_dump(comment_reply_link('', $comment->comment_ID, $post->ID)); ?>
        </div>
    </section>
<?php }

endif;
?> 

<?php
if (is_user_logged_in())
{
    echo "<div class='left comment-box'>";
    ?>
    <?php if (comments_open()) : ?>  
    <form action="<?php echo get_option('siteurl'); ?>/wp-comments-post.php" method="post" id="commentform">  
    <?php if ($user_ID) : ?>  
            <p>Logged in as <a href="<?php echo get_option('siteurl'); ?>/wp-admin/profile.php"><?php echo $user_identity; ?></a>. <a href="<?php echo get_option('siteurl'); ?>/wp-login.php?action=logout" title="Log out of this account">Log out &raquo;</a></p>  
            <input name="submit" type="submit" id="submit" tabindex="5" value="Reply" class="comment-reply"/>  
    <?php endif; ?>  
    <?php wp_editor('', 'comment', $settings = array('media_buttons' => true, 'textarea_rows' => 10)); ?>


        <input type="hidden" name="comment_post_ID" value="<?php echo $id; ?>" /></p>  
    <?php do_action('comment_form', $post->ID); ?>  
    </form>  

<?php else : ?>  
    <p>The comments are closed.</p>  
<?php endif; ?>  

<?php
echo "</div>";
}else
{
?>
 <div class="post-thread">
    <center>
        <div class="sfbutton">
            <a href="#" onclick=' fb_login("<?php echo get_permalink($post->ID) ?>");'>     </a>
        </div>
    </center>
</div>
<?php
}?>

You can see

var_dump(comment_reply_link('', $comment->comment_ID, $post->ID));)

Every time i got null , I also enable the nested reply for 5 level but still got null from that function