diff --git a/core/attributedef.class.inc.php b/core/attributedef.class.inc.php
index 2e5485a66..a41132462 100644
--- a/core/attributedef.class.inc.php
+++ b/core/attributedef.class.inc.php
@@ -3448,6 +3448,11 @@ class AttributeMetaEnum extends AttributeEnum
 		return array('allowed_values', 'sql', 'default_value', 'mapping');
 	}
 
+	public function IsNullAllowed()
+	{
+		return false; // Well... this actually depends on the mapping
+	}
+
 	public function IsWritable()
 	{
 		return false;