I'm trying to set the custom form value on a record to null so it will revert to the default value. I've tried a straight record.SubmitFields setting it to empty string:

record.submitFields({type: 'customrecord_rr_contract', id: contract_id, values: {customform: ''}});

And I've also tried adding it to a nullField list:

contract_record = record.load({type: "customrecord_rr_contract", id: contract_id});
var arrNullFields = ["customform"];
contract_record.nullFieldList = arrNullFields;
contract_record.save();

Neither have an effect. I must be missing something silly but I'm not sure what.