One field incorrectly defaulting to wrong value

We have a custom function which converts potentials to a live account (cctv site) . One field isn't transferring properly and I can't work out why.

The coding is as follows;

void CreateCCTVsitesRecord (int potentialId ) Edit Arguments

potDetails = zoho.crm.getRecordById("Potentials" ,input.potentialId ) ;

mp = map() ;

mp.put("CustomModule2 Name",ifnull(potDetails.get("Potential Name"),""));

mp.put("From Potential_ID",input.potentialId);

mp.put("Main Stakeholder_ID",ifnull(potDetails.get("CONTACTID"),""));

mp.put("CustomModule2 Owner",ifnull(potDetails.get("Potential Owner"),""));

mp.put(("Account_ID"),ifnull(potDetails.get("ACCOUNTID"),""));

mp.put("Install Co._ID",ifnull(potDetails.get("Install Co_ID"),""));

mp.put("Site Type (Industry)",ifnull(potDetails.get("Customer Industry"),""));

etc etc

The other lines seem to work apart from the one in yellow, which defaults to a certain person. I was wondering if this is because it appears as a drop down field and so as a result is never null? How can I fix this?

thanks,

Helen