Populating bill to contact name using OM Extension

Hi Gurus -

I am looking to use OM Extension to populate the bill to contact name at the order line level - since the lines are overridden and users do not want to change values on all lines. I am able to select the header level value for bill to contact name however getting an error that indicates that extension cannot assign a value.

Does anyone know how this can be achieved.

Below is what I have currently in extension

import oracle.apps.scm.doo.common.extensions.ValidationException;

import oracle.apps.scm.doo.common.extensions.Message;

List<Message> messages = new ArrayList<Message>();