Index: question/type/shortanswer/backup/moodle2/restore_qtype_shortanswer_plugin.class.php
===================================================================
RCS file: /cvsroot/moodle/moodle/question/type/shortanswer/backup/moodle2/restore_qtype_shortanswer_plugin.class.php,v
retrieving revision 1.2
diff -u -r1.2 restore_qtype_shortanswer_plugin.class.php
--- question/type/shortanswer/backup/moodle2/restore_qtype_shortanswer_plugin.class.php 9 Jun 2011 02:10:09 -0000       1.2
+++ question/type/shortanswer/backup/moodle2/restore_qtype_shortanswer_plugin.class.php 7 Feb 2012 06:57:06 -0000
@@ -75,6 +75,10 @@
             // Map sequence of question_answer ids
             $answersarr = explode(',', $data->answers);
             foreach ($answersarr as $key => $answer) {
+                //Postgresql does not handle empty strings as integer values
+                if ($answer == '') {
+                  $answer = null;
+                }
                 $answersarr[$key] = $this->get_mappingid('question_answer', $answer);
             }
             $data->answers = implode(',', $answersarr);