Revert "Fixed issue #14050: Unable to import all responses if startda…

…te added"

This reverts commit 6ed9872.

application/helpers/admin/activate_helper.php

@@ -301,10 +301,8 @@ function activateSurvey($iSurveyID, $simulate = false)
                 $aTableDefinition[$aRow['fieldname']] = "pk";
                 break;
             case "startdate":
-                $aTableDefinition[$aRow['fieldname']] = "datetime NULL";
-                break;
             case "datestamp":
-                $aTableDefinition[$aRow['fieldname']] = "datetime NULL";
+                $aTableDefinition[$aRow['fieldname']] = "datetime NOT NULL";
                 break;
             case "submitdate":
                 $aTableDefinition[$aRow['fieldname']] = "datetime";