code: public static void deregister() throws SQLException {
      if (!isRegistered()) {
        throw new IllegalStateException(
            "Driver is not registered (or it has not been registered using Driver.register() method)");
      }
      registeredDriver.closeSpanner();
      DriverManager.deregisterDriver(registeredDriver);
      registeredDriver = null;
    }
docs: According to JDBC specification, this driver is registered against {@link DriverManager} when
  the class is loaded. To avoid leaks, this method allow unregistering the driver so that the
  class can be gc'ed if necessary.
  
  @throws IllegalStateException if the driver is not registered
  @throws SQLException if deregistering the driver fails