From e62e473d44494808e584383af24f8d219f8fc745 Mon Sep 17 00:00:00 2001
From: Frederic Massart <fred@moodle.com>
Date: Fri, 19 Apr 2013 11:04:34 +0800
Subject: [PATCH] MDL-30940 form: Mutiple select work correctly without any
 selection

---
 lib/form/select.php | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/form/select.php b/lib/form/select.php
index 6d17686b146..8b0beba3920 100644
--- a/lib/form/select.php
+++ b/lib/form/select.php
@@ -71,13 +71,19 @@ class MoodleQuickForm_select extends HTML_QuickForm_select{
      * @return string
      */
     function toHtml(){
+        $html = '';
+        if ($this->getMultiple()) {
+            // Adding an hidden field forces the browser to send an empty data even though the user did not
+            // select any element. This value will be cleaned up in self::exportValue() as it will not be part
+            // of the select options.
+            $html .= '<input type="hidden" name="'.$this->getName().'" value="_qf__force_multiselect_submission">';
+        }
         if ($this->_hiddenLabel){
             $this->_generateId();
-            return '<label class="accesshide" for="'.$this->getAttribute('id').'" >'.
-                        $this->getLabel().'</label>'.parent::toHtml();
-        } else {
-             return parent::toHtml();
+            $html .= '<label class="accesshide" for="'.$this->getAttribute('id').'" >'.$this->getLabel().'</label>';
         }
+        $html .= parent::toHtml();
+        return $html;
     }
 
     /**