I have this error System.NullReferenceException: ‘Object reference not set to an instance of an object.’, i make debugging and ex.InnerException.Message give this exception.

 try
    {

        using (SqlConnection con = new SqlConnection(conString))
        {

            string query = "INSERT INTO  CARS(CarsType,CarsPrice)VALUES (@CarsType,@CarsPrice)";
            con.Open();
            SqlCommand command = new SqlCommand(interrogation, connection);
            command.Parameters.AddWithValue("@CarsType" ,"BMW");
            command.Parameters.AddWithValue("@CarsPrice", 10.000);
            command.ExecuteNonQuery();

            command.Parameters.Clear();
            command.Parameters.AddWithValue("@CarsType", "Mercedes");
            command.Parameters.AddWithValue("@CarsPrice", 20.000);
            command.ExecuteNonQuery();

            command.Parameters.Clear();
            command.Parameters.AddWithValue("@CarsType", "Fiat");
            command.Parameters.AddWithValue("@CarsPrice", 80.000);
            command.ExecuteNonQuery();
        }
    }
    catch(Exception ex)
    {
        MessageBox.Show($"Error {ex.Message} source : {ex.Source} ex intern {ex.InnerException.Message}");
    }
}