Attribute definition

Hello

We create an attribute on Physical Prodcut, with a list of choice, and one value is '' (empty), which is the default value.

When the id card of the object is displayed, the value displayed for the attribute is "(empty)", which is not a choice in the choice list. So the system throw an error : '(empty)' violates range for attribute ...

Could you help me to know what i have done wrong ?

Regards