title: Android marshmallow Notification issue
body: <p>My following code on generating the notification works well on Android 3.x, 4.x and 5.x. </p>
  
  <pre><code>    this.builder = new NotificationCompat.Builder(this)
              .setPriority(Notification.PRIORITY_MAX)
              .setDefaults(Notification.DEFAULT_LIGHTS | Notification.DEFAULT_VIBRATE)
              .setSmallIcon(iconId)
              .setContentTitle(getString(R.string.app_name))
              .setStyle(new NotificationCompat.BigTextStyle().bigText(message))
              .setAutoCancel(true)
              .setCategory(Notification.CATEGORY_MESSAGE)
              .setContentText(message);
      this.builder.setContentIntent(pendingIntent);
  </code></pre>
  
  <p>However I got the following exception when I launch it on a Android 6.x device.</p>
  
  <p>java.lang.IllegalArgumentException: Invalid notification (no valid small icon): Notification(pri=2 contentView=[appname]/0x1090085 vibrate=default sound=null defaults=0x6 flags=0x11 color=0x00000000 category=msg vis=PRIVATE)</p>
  
  <p>I have already included notification icons with size 
  25 x 25, 38 x 38, 50 x 50 and 75 x 75 in my drawable folders. </p>
  
  <p>The code works perfectly before, just crashed the app with the exception on marshmallow. </p>
  
  <p>Can any one help?
  Thanks.</p>