Object reference not set to an instance of an object: PlayGamesPlatform

Hello I am facing problem when sending event.

Player auth is successful. But i can not send event

PlayGamesPlatform.Instance.Events.IncrementEvent gives error…

NullReferenceException: Object reference not set to an instance of an object

Why is the null PlayGamesPlatform variable?

version GooglePlayGamesPlugin-0.9.50
Unity 2017.3.1f1

void Start () {
// Create client configuration
PlayGamesClientConfiguration config = new
PlayGamesClientConfiguration.Builder()
.Build();

// Enable debugging output (recommended)
PlayGamesPlatform.DebugLogEnabled = true;

// Initialize and activate the platform
PlayGamesPlatform.InitializeInstance(config);
PlayGamesPlatform.Activate();

SignIn();

PlayGamesPlatform.Instance.Events.IncrementEvent(GPGSIds.event_openedxtimes, 1);

}

Also I tried this:

private static readonly PlayGamesClientConfiguration config = new
        PlayGamesClientConfiguration.Builder()
        .Build();

void Start () {

    // Enable debugging output (recommended)
    PlayGamesPlatform.DebugLogEnabled = true;

    // Initialize and activate the platform
    PlayGamesPlatform.InitializeInstance(config);
    PlayGamesPlatform.Activate();

    SignIn();

    PlayGamesPlatform.Instance.Events.IncrementEvent(GPGSIds.event_openedxtimes, 1);
}

Regards.

Try to put initialization of PlayGamesPlatform to Awake method.