Customer Import FBDI DFF to update with null or blank value

I am using Customer Import FBDI to update TCA Customer Accounts descriptive flexfields (DFF, e.g. attribute14 in HZ_CUST_ACCOUNTS table) with blank or null value. It is in Oracle Fusion SaaS. in the attribute fields in the FBDI what value should I populate to update the DFF as blank in the fusion table.

I tried below values but nothing worked:

#NULL

!NULL

Via SOAPui WSDL, it's possible but, I have huge records to be updated hence, xls based FBDI has to be used.

Kindly suggest.