连接必须是有效且打开的(executeScalar())

给我这个错误connection must be valid and open，我不知道如何解决它。

    private void loginUtenti(string user, string psw)
    {
        createConnection(); 
        string connectionString = "server=localhost;user=root;database=test;port=3306;password=******;"; ;
        MySqlConnection connection = new MySqlConnection(connectionString);
        command = new MySqlCommand();
        command.CommandText = "SELECT Psw FROM Utenti WHERE Nome = '" + user + "';";
        object passwordInput = command.ExecuteScalar(); // error "connection must be valid and open" 
        string nullo = "";