create new property type using ssml

Question

Hello,

I want to create a new property type like

<td><ss:edit source="$customer.bestfriend" size="20"/></td>

But I get this error

Account Form
ERROR: Source string "$customer.bestfriend" is not valid. The property or method 
does not exist (com.kurant.storesense.metadata.PropertyNotFoundException: Class 
Customer does not have a property named 'bestfriend'.). (787-831);

Thanks Jean