return default value when user not input

return default value when user not input field
var (
notes ='this will be default'
)

qapi := `
UPDATE custom_param SET param_value = $1, start_date = $2, end_date = $3, status = $4 `enter code here` WHERE param_name = 'default-password'
RETURNING param_value, start_date, end_date, status, notes; 
`
// insrt into master_param
sqlError := tx.QueryRowContext(ctx, qapi, request.Value, request.StartDate, request.EndDate, request.Status, request.Notes).Scan(
	&value,
	&startDate,
	&endDate,
	&status,
	&notes,
)
queryInsertNotes := `insert `
if request.Notes != "" {
	notes = request.Notes
}

if sqlError != nil {
	log.Println("SQL Error on ReadApplication on UpdateScheduleMaintenance", sqlError)
	tx.Rollback()
	return schedule, sqlError
}

err = tx.Commit()
if err != nil {
	tx.Rollback()
	return schedule, err
}

return default notes when user not inputs any notes

I think you need something like this, haven't tested the code but you get the idea.

notes := "this will be default"
if request.Notes != "" {
    notes = request.Notes
}

qapi := `
UPDATE custom_param SET param_value = $1, start_date = $2, end_date = $3, status = $4, notes = $4 WHERE param_name = 'default-password'
RETURNING param_value, start_date, end_date, status, notes; 
`
// insrt into master_param
sqlError := tx.QueryRowContext(ctx, qapi, request.Value, request.StartDate, request.EndDate, request.Status, notes).Scan(
    &value,
    &startDate,
    &endDate,
    &status,
    &notes,
)


if sqlError != nil {
    log.Println("SQL Error on ReadApplication on UpdateScheduleMaintenance", sqlError)
    tx.Rollback()
    return schedule, sqlError
}

err = tx.Commit()
if err != nil {
    tx.Rollback()
    return schedule, err
}