Passing blank value using BUS0015 BAPI

I am using BUS0015 BAPI via LSMW to assign and unassign company codes from profit centers.

I can successfully assign a company code by passing a 'X' in the 'ASSIGN_TO_PRCTR' field mapping for structures 'E1BP0015_7' and 'E1BP0015_7X'.

However I cannot unassign. I have tried inputting:

• ' '
• '!'
• '/'
• '#'
• ALT '0160' which is the ASCII value of a space.

Can anyone please assist?