Custom category page for Genesis Framework

category-custom.php

<?php

/* Add the featured image after post title
------------------------------------------------------------ */

add_action( 'genesis_before_post_title', 'jm_portfolio_grid' );
function jm_portfolio_grid() {
    if ( has_post_thumbnail() ){
        echo '<a class="alignleft" href="' . get_permalink() .'" title="' . the_title_attribute( 'echo=0' ) . '">';
        echo get_the_post_thumbnail($thumbnail->ID, 'thumbnail', array('class' => 'alignleft'));
        echo '</a>';
    }
}