Service Mapping- OM to AR Expression with a condition

Dear All,

We have a requirement to update the AR Invoice Conversion Rate as Order Creation date for specific currency Orders.. When we directly map the attribute from VO we were able to achieve this. But when we wanted to have the Currency condition through the below Expression it is again taking the System Date. Can you please let us know if there is any change required in the condition to achieve the requirement. Our Currency is 'NGN'.

(TransactionalCurrencyCode.equals('NGN'))? CreationDate: null

Thanks & Regards,

Sai Kumar.