Calling Yoast SEO title in widget not work

Question

I install Wordpress SEO plugin by Yoast, test the title re-write function and it works in my title bar (single post). However when I try to call the title in widget, I just get error message

Warning: Missing argument 1 for kpndg()...

I insert this code in theme functions.php

add_filter( 'wpseo_title', 'kpndg' );
function kpndg( $title )  {
    return $title;
} 

Then call it in my widget:

$out.='<div class="trending-bar add-active bar-' . $i . '">';

    $out.='<a class="trending-link" href="'.get_permalink().'">&nbsp;</a>'; 

    $out.='<div class="title">'.kpndg().'</div>';

    $out.='<div class="trending-color-wrapper">';
        $out.='<div class="trending-color-layer"></div>';
        $out.='<div class="trending-color"></div>';
        $out.='<div class="trending-meta">' . $meta . '</div>';
    $out.='</div>';

$out.='</div>';

I can't figure out what is the problem in that code.