Trying to use a script to add a default vendor when a new Assembly/Serialized Assembly is created.

I'm getting the following error: 


  

org.mozilla.javascript.EcmaError: TypeError: Cannot find function selectNewLine in object standard record.

I'm only including N/record. Here's the relevant bit of code.

            var assemblyRecord = context.newRecord;
            var newVendor = assemblyRecord.selectNewLine({ sublistId: 'itemvendor' });
            assemblyRecord.setCurrentSublistValue({
                sublistId: 'itemvendor',
                fieldId: 'vendor',
                value: vendorId
            });
            assemblyRecord.setCurrentSublistValue({
                sublistId: 'itemvendor',
                fieldId: 'purchaseprice',
                value: pruchasePrice
            });
            assemblyRecord.setCurrentSublistValue({
                sublistId: 'itemvendor',
                fieldId: 'preferredvendor',
                value: true
            });
            assemblyRecord.commitLine({    sublistId: 'itemvendor'    });

Note that the Assembly/Serialized Assembly is being created via a SuiteTalk request that's made during the execution of a different User Event SuiteScript.