diff --git a/application/wizardhelper.class.inc.php b/application/wizardhelper.class.inc.php
index c544044c20..79bcbd0a56 100644
--- a/application/wizardhelper.class.inc.php
+++ b/application/wizardhelper.class.inc.php
@@ -278,12 +278,12 @@ class WizardHelper
 
     public function GetInitialState()
     {
-        return $this->m_aData['m_sInitialState'];
+        return isset($this->m_aData['m_sInitialState']) ? $this->m_aData['m_sInitialState'] : null;
     }
 
     public function GetStimulus()
     {
-        return $this->m_aData['m_sStimulus'];
+        return isset($this->m_aData['m_sStimulus']) ? $this->m_aData['m_sStimulus'] : null;
     }
 	
 	public function GetIdForField($sFieldName)
diff --git a/pages/ajax.render.php b/pages/ajax.render.php
index 3f82323919..fcf8c73d7f 100644
--- a/pages/ajax.render.php
+++ b/pages/ajax.render.php
@@ -578,7 +578,7 @@ try
 			$oObj->Set($sAttCode, $defaultValue);
 		}
 		$sFormPrefix = $oWizardHelper->GetFormPrefix();
-		$aExpectedAttributes = $oObj->GetTransitionAttributes($oWizardHelper->GetStimulus(), $oWizardHelper->GetInitialState());
+		$aExpectedAttributes = ($oWizardHelper->GetStimulus() === null) ? array() : $oObj->GetTransitionAttributes($oWizardHelper->GetStimulus(), $oWizardHelper->GetInitialState());
 		foreach($oWizardHelper->GetFieldsForAllowedValues() as $sAttCode)
 		{
 			$sId = $oWizardHelper->GetIdForField($sAttCode);