/**
  * Echo the invoice expiration_date
  * @param  integer $id
  * @return string
  */
 function si_invoice_expiration_date($id = 0)
 {
     if (!$id) {
         $id = get_the_ID();
     }
     echo apply_filters('si_invoice_expiration_date', date_i18n(get_option('date_format'), si_get_invoice_expiration_date($id)), $id);
 }
 /**
  * Echo the invoice expiration_date
  * @param  integer $id 
  * @return string      
  */
 function si_invoice_expiration_date($id = 0)
 {
     if (!$id) {
         global $post;
         $id = $post->ID;
     }
     echo apply_filters('si_invoice_expiration_date', date_i18n(get_option('date_format'), si_get_invoice_expiration_date($id)), $id);
 }