Correctly handle DateTime values in Vcard export

program/steps/addressbook/export.inc

@@ -131,8 +131,13 @@ function prepare_for_export(&$record, $source = null)
 
         foreach ($record as $key => $values) {
             list($field, $section) = explode(':', $key);
-            foreach ((array)$values as $value) {
-                if (is_array($value) || @strlen($value)) {
+            // avoid casting DateTime objects to array
+            // (same as in rcube_contacts::convert_save_data())
+            if (is_object($values) && is_a($values, 'DateTime')) {
+                $values = array(0 => $values);
+            }
+            foreach ($values as $value) {
+                if (is_array($value) || is_a($value, 'DateTime') || @strlen($value)) {
                     $vcard->set($field, $value, strtoupper($section));
                 }
             }