Update lookup field

Update lookup field

Hi 

I have this function that needs to update the account based on what happens in a custommodule

account = zoho.crm._getRecordById("Accounts",account_id);
trial = zoho.crm._getRecordById("CustomModule2",trial_id);
trialLookup = trial.get("Name");

StartNote = trial.get("Start trial note");
MidNote = trial.get("Mid trial note");
EndNote = trial.get("End trial note");

account.put("Start trial note",StartNote);
account.put("Mid trial note",MidNote);
account.put("End trial note",EndNote);
account.put("Trial",trialLookup);

crmResp = zoho.crm._updateRecord("Accounts",account_id.toString(),account);

It can update the first 3 fields but only updates the account.put("Trial",trialLookup) if the field is empty. The field I am trying to update is a lookup field. Is there anyway to force the update or empty the field before updating it again?

Thanks