DriverLicenseSmartField { // client
  getConfiguredLookupCall() {
    return DriverLicenseLookupCall.class;
  }
}

DriverLicenseLookupCall { // shared
  getConfiguredService() {
    return IDriverLicenseLookupService.class;
  }
}

DriverLicenseLookupService implements IDriverLicenseLookupService { // server
  getDataByText(call) {
    // implement the specific logic to find a driver license by text here and return a collection of results having text _and_ key
  }
}

      // Driver's license SmartField
      if (!StringUtility.isNullOrEmpty(employee.driversLicense().get())) {
        // getDriversLicenseField().parseAndSetValue(employee.driversLicense().get());
        getDriversLicenseField().setValueByLookupRow(
            getDriversLicenseField().callTextLookup(employee.driversLicense().get(), 0).get(0));
      }

getDriverLicenseField().setValue(employee.getDriversLicense().getKey());

class DriversLicense {
  Integer getKey() {
    return m_key;
  }
}

class DriverLicenseField extends AbstractSmartField<Integer> { // <-- the generic type must match the type of the key.
}