title: Android app crashes when minifyEnabled is true
body: <p>I am using a multi-module app and the app crashes when <code>minifyEnabled true</code> in the <code>installed</code> module's build.gradle.</p>
  <p>Following is the deobfuscated stacktrace I retrieved from play console.</p>
  <pre><code> FATAL EXCEPTION: ControllerMessenger
  Process: com.packagename, PID: 16978
  java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference
      at com.packagename.login.Utils.AuthenticationActions.saveCredentials(AuthenticationActions.java)
      at com.packagename.login.LoginActivity$1$1.onCompleted(LoginActivity.java)
      at com.packagename.login.LoginActivity$1$1.onCompleted(LoginActivity.java)
      at com.koushikdutta.async.future.SimpleFuture.handleCallbackUnlocked(SimpleFuture.java)
      at com.koushikdutta.async.future.SimpleFuture.setComplete(SimpleFuture.java)
      at com.koushikdutta.async.future.SimpleFuture.setComplete(SimpleFuture.java)
      at com.koushikdutta.ion.IonRequestBuilder$EmitterTransform$1.onCompleted(IonRequestBuilder.java)
      at com.koushikdutta.async.future.SimpleFuture.handleCallbackUnlocked(SimpleFuture.java)
      at com.koushikdutta.async.future.SimpleFuture.setComplete(SimpleFuture.java)
      at com.koushikdutta.async.future.SimpleFuture.setComplete(SimpleFuture.java)
      at com.koushikdutta.ion.IonRequestBuilder$1.run(IonRequestBuilder.java)
      at com.koushikdutta.async.AsyncServer$RunnableWrapper.run(AsyncServer.java)
      at android.os.Handler.handleCallback(Handler.java:746)
      at android.os.Handler.dispatchMessage(Handler.java:95)
      at androidx.test.espresso.base.Interrogator.a(Interrogator.java:19)
      at androidx.test.espresso.base.UiControllerImpl.a(UiControllerImpl.java:166)
      at androidx.test.espresso.base.UiControllerImpl.a(UiControllerImpl.java:158)
      at androidx.test.espresso.base.UiControllerImpl.a(UiControllerImpl.java:34)
      at androidx.test.espresso.action.MotionEvents.a(MotionEvents.java:77)
      at androidx.test.espresso.action.MotionEvents.a(MotionEvents.java:52)
      at androidx.test.espresso.action.Tap.c(Tap.java:8)
      at androidx.test.espresso.action.Tap.b(Tap.java:18)
      at androidx.test.espresso.action.Tap$1.a(Tap.java:3)
      at androidx.test.espresso.action.GeneralClickAction.perform(GeneralClickAction.java:22)
      at androidx.test.espresso.ViewInteraction$SingleExecutionViewAction.perform(ViewInteraction.java:9)
      at androidx.test.espresso.ViewInteraction.a(ViewInteraction.java:79)
      at androidx.test.espresso.ViewInteraction.a(ViewInteraction.java:96)
      at androidx.test.espresso.ViewInteraction$1.call(ViewInteraction.java:3)
      at java.util.concurrent.FutureTask.run(FutureTask.java:237)
      at android.os.Handler.handleCallback(Handler.java:746)
      at android.os.Handler.dispatchMessage(Handler.java:95)
      at android.os.Looper.loop(Looper.java:148)
      at android.app.ActivityThread.main(ActivityThread.java:5459)
      at java.lang.reflect.Method.invoke(Method.java)
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
  </code></pre>
  <p>I am unable to understand what does this code correspond to <code>'java.lang.Object java.util.List.get(int)'</code></p>
  <p>I am using multiple external libraries, one of which is <em>ion koush</em>.</p>
  <p>I have tried adding this to ever proguard-rules.pro file in my project
  <code>-keep class com.koushikdutta.** { *;}</code>. But this didn't yield any success.</p>