jnews_get_primary_category

function jnews_get_primary_category( $post_id ) {
    $category_id = null;

    if ( get_post_type( $post_id ) === 'post' ) {
        $category = vp_metabox( 'jnews_primary_category.id', null, $post_id );
        $cat      = get_term( $category );

        if ( ! empty( $category ) && isset( $cat ) ) {
            $category_id = $category;
        } else {
            $categories = array_slice( get_the_category( $post_id ), 0, 1 );
            if ( empty( $categories ) ) {
                return null;
            }
            $category    = array_shift( $categories );
            $category_id = $category->term_id;
        }
    }

    return apply_filters( 'jnews_primary_category', $category_id, $post_id );
}