Fixed isssue with final class recall, discovered when reintroducing the field Ticket::related_change_id

git-svn-id: http://svn.code.sf.net/p/itop/code/trunk@717 a333f486-631f-4898-b8df-5754b55c2be0

core/attributedef.class.inc.php

@@ -745,6 +745,7 @@ class AttributeClass extends AttributeString
 
 	public function GetAsHTML($sValue)
 	{
+		if (empty($sValue)) return '';
 		return MetaModel::GetName($sValue);
 	}
 
@@ -822,6 +823,7 @@ class AttributeFinalClass extends AttributeString
 
 	public function GetAsHTML($sValue)
 	{
+		if (empty($sValue)) return '';
 		return MetaModel::GetName($sValue);
 	}
 }