Android: Crash when opening other activity

[JulianBissekkou]

Steps to reproduce:

1. MainActivity has a flutter view that draws a map
2. Open another activity (this can be an external webview or some other package that pushes something native)
3. Go back to the MainActivity
4. Crash

StackTrace:

java.lang.RuntimeException: Unable to pause activity {yourpackage.MainActivity}: java.lang.NullPointerException: A null pointer. object cannot be null.
E/AndroidRuntime(10560): 	at android.app.ActivityThread.performPauseActivityIfNeeded(ActivityThread.java:5766)
E/AndroidRuntime(10560): 	at android.app.ActivityThread.performPauseActivity(ActivityThread.java:5717)
E/AndroidRuntime(10560): 	at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:5669)
E/AndroidRuntime(10560): 	at android.app.servertransaction.PauseActivityItem.execute(PauseActivityItem.java:60)
E/AndroidRuntime(10560): 	at android.app.servertransaction.ActivityTransactionItem.execute(ActivityTransactionItem.java:63)
E/AndroidRuntime(10560): 	at android.app.servertransaction.TransactionExecutor.executeLifecycleItem(TransactionExecutor.java:169)
E/AndroidRuntime(10560): 	at android.app.servertransaction.TransactionExecutor.executeTransactionItems(TransactionExecutor.java:101)
E/AndroidRuntime(10560): 	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:80)
E/AndroidRuntime(10560): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2773)
E/AndroidRuntime(10560): 	at android.os.Handler.dispatchMessage(Handler.java:109)
E/AndroidRuntime(10560): 	at android.os.Looper.loopOnce(Looper.java:232)
E/AndroidRuntime(10560): 	at android.os.Looper.loop(Looper.java:317)
E/AndroidRuntime(10560): 	at android.app.ActivityThread.main(ActivityThread.java:8934)
E/AndroidRuntime(10560): 	at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime(10560): 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:591)
E/AndroidRuntime(10560): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:911)
E/AndroidRuntime(10560): Caused by: java.lang.NullPointerException: A null pointer. object cannot be null.
E/AndroidRuntime(10560): 	at com.arcgismaps.internal.ErrorFactoryKt.toPlatformExceptionOrNull(ErrorFactory.kt:212)
E/AndroidRuntime(10560): 	at com.arcgismaps.internal.ErrorFactoryKt.convertToPublic(ErrorFactory.kt:111)
E/AndroidRuntime(10560): 	at com.arcgismaps.internal.ErrorFactory.createThrowableFromCoreError(ErrorFactory.kt:59)
E/AndroidRuntime(10560): 	at com.arcgismaps.internal.jni.CoreGeoView.nativePause(Native Method)
E/AndroidRuntime(10560): 	at com.arcgismaps.internal.jni.CoreGeoView.pause(CoreGeoView.java:680)
E/AndroidRuntime(10560): 	at com.arcgismaps.mapping.view.GeoView.pause(GeoView.kt:1224)
E/AndroidRuntime(10560): 	at com.arcgismaps.mapping.view.GeoView.access$pause(GeoView.kt:106)
E/AndroidRuntime(10560): 	at com.arcgismaps.mapping.view.GeoView$RenderingThread.pause(GeoView.kt:1778)
E/AndroidRuntime(10560): 	at com.arcgismaps.mapping.view.MapView.onPause(MapView.kt:968)
E/AndroidRuntime(10560): 	at androidx.lifecycle.DefaultLifecycleObserverAdapter.onStateChanged(DefaultLifecycleObserverAdapter.kt:27)
E/AndroidRuntime(10560): 	at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.jvm.kt:320)
E/AndroidRuntime(10560): 	at androidx.lifecycle.LifecycleRegistry.backwardPass(LifecycleRegistry.jvm.kt:272)
E/AndroidRuntime(10560): 	at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.jvm.kt:289)
E/AndroidRuntime(10560): 	at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.jvm.kt:142)
E/AndroidRuntime(10560): 	at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.jvm.kt:124)
E/AndroidRuntime(10560): 	at androidx.fragment.app.Fragment.performPause(Fragment.java:3323)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentStateManager.pause(FragmentStateManager.java:684)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:310)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:114)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1614)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3198)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentManager.dispatchPause(FragmentManager.java:3134)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentController.dispatchPause(FragmentController.java:296)
E/AndroidRuntime(10560): 	at androidx.fragment.app.FragmentActivity.onPause(FragmentActivity.java:284)
E/AndroidRuntime(10560): 	at android.app.Activity.performPause(Activity.java:9294)
E/AndroidRuntime(10560): 	at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1781)
E/AndroidRuntime(10560): 	at android.app.ActivityThread.performPauseActivityIfNeeded(ActivityThread.java:5756)
E/AndroidRuntime(10560): 	... 15 more