PHP Warning

hello,

i got a PHP warning when i click on ADD(or Remove) favorite link on post page.

Warning: Creating default object from empty value in /home/wp-content/plugins/wp-favorite-posts/wp-favorite-posts.php on line 152

the plugin is working just fine but i’ll appreciate it if you guys could give me a hint on how can fix this so the warning message goes away.

here is the line of codes that the warning message is referring to :

function wpfp_link( $return = 0, $action = "", $show_span = 1, $args = array() ) {
    global $post;
    //print_r($post);
    $post_id = &$post->ID;    <=== This is the line 152
    extract($args);
    $str = "";
    if ($show_span)
        $str = "<span class='wpfp-span'>";
    $str .= wpfp_before_link_img();
    $str .= wpfp_loading_img();
    if ($action == "remove"):
        $str .= wpfp_link_html($post_id, wpfp_get_option('remove_favorite'), "remove");
    elseif ($action == "add"):
        $str .= wpfp_link_html($post_id, wpfp_get_option('add_favorite'), "add");
    elseif (wpfp_check_favorited($post_id)):
        $str .= wpfp_link_html($post_id, wpfp_get_option('remove_favorite'), "remove");
    else:
        $str .= wpfp_link_html($post_id, wpfp_get_option('add_favorite'), "add");
    endif;
    if ($show_span)
        $str .= "</span>";
    if ($return) { return $str; } else { echo $str; }
}

Thanks