GcmNetworkManager.getInstance(Context context) returns null

Question

I am looking for a solution for days. I searched through many posts but I did not find a answer for my problem. I am using GCM Network Manager for my app, I followed several tutorials if what I did was correct. Everything seems correct but when I call GcmNetworkManager.getInstance(Context context) it returns me null. Then when I call an one off task it does nothing. I get no error but nothing happens. Here is the code :

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_awesome_activity);

    gcmNetworkManager = GcmNetworkManager.getInstance(this);

    WardrobeElement newElement = new WardrobeElement(1, 3, 'test');

    Bundle extras = new Bundle();
    extras.putSerializable(Constants.SERIALIZED_WARDROBE_ELEMENT_KEY, newElement);

    Task task = new OneoffTask.Builder()
                    .setService(GCMService.class)
                    .setExecutionWindow(0, 30)
                    .setTag(Constants.MY_TAG)
                    .setUpdateCurrent(false)
                    .setRequiredNetwork(Task.NETWORK_STATE_CONNECTED)
                    .setRequiresCharging(false)
                    .setExtras(extras)
                    .build();

    gcmNetworkManager.schedule(task);

    //gcmNetworkManager = null
}

In my manifest :

<service android:name="fr.hexus.dresscode.classes.GCMService"
    android:permission="com.google.android.gms.permission.BIND_NETWORK_TASK_SERVICE"
    android:exported="true">
    <intent-filter>
        <action android:name="com.google.android.gms.gcm.ACTION_TASK_READY"/>
    </intent-filter>
</service>

And my class that implements GCM Network Manager :

public class GCMService extends GcmTaskService
{
    @Override
    public int onRunTask(TaskParams taskParams)
    {
        if(Constants.MY_TAG.equals(taskParams.getTag()))
        {
            final Bundle extras = taskParams.getExtras();
            final WardrobeElement currentElement = (WardrobeElement) extras.getSerializable(Constants.SERIALIZED_WARDROBE_ELEMENT_KEY);

            try
            {
                currentElement.sendWardrobeElementToTheAPI();
                return GcmNetworkManager.RESULT_SUCCESS;

            } catch(CallException exception)
            {
                return GcmNetworkManager.RESULT_RESCHEDULE;
            }
        }

        return 0;
    }
}

I hope you can help me to find a way to solve this.

Thank you

Edit : I solved my problem by replacing GCM Network Manager by Firebase Job Dispatcher, it's almost the same but it works for me. I suspect GCM Network Manager is no longer compatible as it is deprecated since April 2018. Firebase Job Dispatcher seems to be its substitute.