title: Firebase Notification Always shows blank icon
body: <p>I'm new with <strong>FCM</strong>. I cannot make <strong>FCM</strong> use my app icon as notification icon and the icon is always a white blank one.</p>
  
  <p>I imported an icon to <code>mipmap</code> folders but nothing seems changed. As some dude say that this is because of lollipop notification as <a href="https://stackoverflow.com/questions/28387602/notification-bar-icon-turns-white-in-android-5-lollipop">in this question</a></p>
  
  <p>But the problem is, the <strong>FCM</strong> notification automatically pops up and I cannot get the Notification builder to override the icon. How can I change it?</p>