'Some modules, such as Purchase, provide a feature to add automatically pre-filled
invoice lines. However, these modules might not be aware of extra fields which are
added by extensions of the accounting module.
This method is intended to be overridden by these extensions, so that any new field can
easily be auto-filled as well.
:param invoice : account.invoice corresponding record
:rtype line : account.invoice.line record'

def _set_additional_fields(self, invoice):

    pass
