commit 415aef24aba27abcccfee588a104d5f0d3238b58
Author: ccarigna <chris.carignan@gmail.com>
Date:   Fri Dec 12 18:37:35 2014 -0500

    Support the 'required' field option. https://www.drupal.org/node/2327235

diff --git a/commerce_currency.module b/commerce_currency.module
index afb34c5..92c00bb 100644
--- a/commerce_currency.module
+++ b/commerce_currency.module
@@ -98,7 +98,7 @@ function commerce_currency_field_widget_form(&$form, &$form_state, $field, $inst
   switch ($instance['widget']['type']) {
     case 'commerce_currency':
       // Build a currency options list from all enabled currencies.
-      $options = array("_none" => t("- Select value -"));
+      $options = $element['#required'] ? array() : array("_none" => t("- Select value -"));
 
       foreach (commerce_currencies(TRUE) as $currency_code => $currency) {
         $options[$currency_code] = _commerce_currency_format_currency($currency);
@@ -110,6 +110,7 @@ function commerce_currency_field_widget_form(&$form, &$form_state, $field, $inst
         '#description' => $element['#description'],
         '#options' => $options,
         '#default_value' => isset($items[$delta]['currency_code']) ? $items[$delta]['currency_code'] : "_none",
+        '#required' => $element['#required'],
       );
       break;
   }