title: Firebase can't find referenced method
body: <p>I get the following errors when building an APK with ProGuard:</p>
  
  <p><a href="https://i.stack.imgur.com/lX90G.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lX90G.png" alt="enter image description here"></a></p>
  
  <p>ProGuard is using the default proguardfile and yet this issue has just appeared. How can I resolve this?</p>