Duplicate content in WordPress plugin vs code

// Duplicates a post as draftand takes the user to the editor screen
function rd_duplicate_post_as_draft(){
global $wpdb;
if (!(isset($_GET['post']) || isset($_POST['post']) ||
(isset($_REQUEST['action']) && 'rd_duplicate_post_as_draft' == $_REQUEST['action']))) {
wp_die('There was no selected entry!');
}
// Checking nonce 
if (!isset($_GET['duplicate_nonce'] ) ||
!wp_verify_nonce($_GET['duplicate_nonce'], basename( __FILE__ ))) {
return;
}
// Obtain the original post id
$post_id = (isset($_GET['post']) ? absint($_GET['post']) : absint($_POST['post']));
// and its data
$post = get_post($post_id);
// make the current user the author of the entry
$current_user = wp_get_current_user();
$new_post_author = $current_user->ID;
// if the entry has data we create the duplicate
if (isset( $post ) && $post != null) {
$args = array(
'comment_status' => $post->comment_status,
'ping_status'    => $post->ping_status,
'post_author'    => $new_post_author,
'post_content'   => $post->post_content,
'post_excerpt'   => $post->post_excerpt,
'post_name'      => $post->post_name,
'post_parent'    => $post->post_parent,
'post_password'  => $post->post_password,
'post_status'    => 'draft',
'post_title'     => $post->post_title,
'post_type'      => $post->post_type,
'to_ping'        => $post->to_ping,
'menu_order'     => $post->menu_order
);
// insert the entry using the function wp_insert_post()
$new_post_id = wp_insert_post($args);
// obtain taxonomies of the original and addit to the duplicate
$taxonomies = get_object_taxonomies($post->post_type);
foreach ($taxonomies as $taxonomy) {
$post_terms = wp_get_object_terms($post_id, $taxonomy, array('fields' => 'slugs'));
wp_set_object_terms($new_post_id, $post_terms, $taxonomy, false);
}
// duplicate metadata
$post_meta_infos = $wpdb->get_results("SELECT meta_key, meta_value FROM $wpdb->postmeta WHERE post_id=$post_id");
if (count($post_meta_infos)!=0) {
$sql_query = "INSERT INTO $wpdb->postmeta (post_id, meta_key, meta_value) ";
foreach ($post_meta_infos as $meta_info) {
$meta_key = $meta_info->meta_key;
if( $meta_key == '_wp_old_slug' ) {continue;}
$meta_value = addslashes($meta_info->meta_value);
$sql_query_sel[]= "SELECT $new_post_id, '$meta_key', '$meta_value'";
}
$sql_query.= implode(" UNION ALL ", $sql_query_sel);
$wpdb->query($sql_query);
}
// finally redirect user to the edit screen
wp_redirect( admin_url( 'post.php?action=edit&post=' . $new_post_id ) );
exit;
} else {
wp_die('Error when creating entry, the original could not be found: ' . $post_id);
}
}
add_action( 'admin_action_rd_duplicate_post_as_draft', 'rd_duplicate_post_as_draft' );
// Create the corresponding links
function rd_duplicate_post_link( $actions, $post ) {
if (current_user_can('edit_posts')) {
$actions['duplicate'] = '<a href="'
. wp_nonce_url('admin.php?action=rd_duplicate_post_as_draft&post='
. $post->ID, basename(__FILE__), 'duplicate_nonce' )
. '" title="Duplicate as draft" rel="permalink">Duplicate as draft</a>';
}
return $actions;
}
// and add them to the list of pagesand entries
add_filter( 'post_row_actions', 'rd_duplicate_post_link', 10, 2 );
add_filter('page_row_actions', 'rd_duplicate_post_link', 10, 2);