*Fix bug#20452

module/task/config.php

@@ -35,7 +35,7 @@ $config->task->exportFields = '
     openedBy, openedDate, assignedTo, assignedDate,
     finishedBy, finishedDate, canceledBy, canceledDate,
     closedBy, closedDate, closedReason,
-    lastEditedBy, lastEditedDate,files
+    lastEditedBy, lastEditedDate, avtivatedDate, files
     ';
 
 $config->task->customCreateFields      = 'story,estStarted,deadline,mailto,pri,estimate';

module/task/model.php

@@ -3287,7 +3287,7 @@ class taskModel extends model
                 echo substr($task->lastEditedDate, 5, 11);
                 break;
             case 'activatedDate':
-                echo substr($task->activatedDate, 5, 11);
+                echo helper::isZeroDate($bug->activatedDate) ? '' : substr($task->activatedDate, 5, 11);
                 break;
             case 'actions':
                 if($storyChanged)