title: Android notification icon is a white circle
body: <p>I've got a strange problem with notification icon today.</p>
  
  <p>It looks like this :
  <a href="https://i.stack.imgur.com/zCfc3.png" rel="noreferrer"><img src="https://i.stack.imgur.com/zCfc3.png" alt="enter image description here"></a>
  (the white circle ...)</p>
  
  <p>Did I do something bad ?</p>
  
  <pre><code>Uri defaultSoundUri= RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
  NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
                  .setSmallIcon(R.drawable.icon_notification)
                  .setContentTitle(this.getString(R.string.notification_title))
                  .setContentText(this.getString(R.string.notification_text))
                  .setAutoCancel(true)
                  .setSound(defaultSoundUri)
                  .setContentIntent(pendingIntent);
  </code></pre>
  
  <p>Here is my icon image (freshly downloaded from here <a href="https://material.io/icons/#ic_photo" rel="noreferrer">https://material.io/icons/#ic_photo</a>) :
  <a href="http://image.noelshack.com/fichiers/2016/44/1478185219-icon-notification.png" rel="noreferrer">http://image.noelshack.com/fichiers/2016/44/1478185219-icon-notification.png</a></p>
  
  <p>Did I miss something ?</p>
  
  <p>For the record, I'm using SDK 24 and only created the <code>hdpi</code> resource folder for now.</p>
  
  <p>Edit #1 : I've added the <code>ldpi</code>, <code>mdpi</code> and <code>xhdpi</code> icons, nothing change ...</p>
  
  <p>Edit #2 : For more precision, I'm trying to create this notification from a service ... FCM messaging service ...</p>