AT61 1904 3002 3457 3201 is indicated as valid, missing BIC is not reported to user.
Acceptance Criteria derived from @Jan_Dittrich's comment:
- Change the label of the field BIC to BIC (Optional)
- Show validity indicator if the field contains a valid value (according to ISO_9362, see data-pattern attribute of the field in the other skin)
- Don't show a validity indicator if empty