Exception with Maps

Get the following exception when attempting to use maps:

Java.Lang.RuntimeException: java.lang.reflect.InvocationTargetException
  at --- End of managed exception stack trace ---
  at java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
  at at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
  at Caused by: java.lang.reflect.InvocationTargetException
  at at java.lang.reflect.Method.invoke(Native Method)
  at at java.lang.reflect.Method.invoke(Method.java:372)
  at at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
  at ... 1 more
  at Caused by: md52ce486a14f4bcd95899665e9d932190b.JavaProxyThrowable: System.NullReferenceException: Object reference not set to an instance of an object
  at at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () <IL 0x00011, 0x0004b>
  at Android.Runtime.JNIEnv.CallVoidMethod (intptr,intptr,Android.Runtime.JValue*) [0x00063] in /Users/builder/data/lanes/monodroid-mavericks-monodroid-5.1-series/d419c934/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:571
  at Android.Views.ViewGroup.Layout (int,int,int,int) [0x00082] in /Users/builder/data/lanes/monodroid-mavericks-monodroid-5.1-series/d419c934/source/monodroid/src/Mono.Android/platforms/android-21/src/generated/Android.Views.ViewGroup.cs:3760
  at at Xamarin.Forms.Platform.Android.VisualElementTracker.UpdateLayout () <IL 0x0009b, 0x0029e>
  at at Xamarin.Forms.Platform.Android.MasterDetailRenderer.UpdateLayout () <IL 0x0000e, 0x0003b>
  at at Xamarin.Forms.Platform.Android.Platform.OnLayout (bool,int,int,int,int) <IL 0x000a0, 0x0039b>
  at at Xamarin.Forms.Platform.Android.PlatformRenderer.OnLayout (bool,int,int,int,int) <IL 0x0001b, 0x00097>
  at Android.Views.ViewGroup.n_OnLayout_ZIIII (intptr,intptr,bool,int,int,int,int) [0x00009] in /Users/builder/data/lanes/monodroid-mavericks-monodroid-5.1-series/d419c934/source/monodroid/src/Mono.Android/platforms/android-21/src/generated/Android.Views.ViewGroup.cs:4041
  at at (wrapper dynamic-method) object.790a1593-347b-4654-b3bc-aacc95f2d37d (intptr,intptr,bool,int,int,int,int) <IL 0x0002f, 0x0005b>
  at at md5530bd51e982e6e7b340b73e88efe666e.PlatformRenderer.n_onLayout(Native Method)
  at at md5530bd51e982e6e7b340b73e88efe666e.PlatformRenderer.onLayout(PlatformRenderer.java:62)
  at at android.view.View.layout(View.java:15671)
  at at android.view.ViewGroup.layout(ViewGroup.java:5038)
  at at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
  at at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1692)
  at at android.widget.LinearLayout.onLayout(LinearLayout.java:1468)
  at at android.view.View.layout(View.java:15671)
  at at android.view.ViewGroup.layout(ViewGroup.java:5038)
  at at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
  at at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
  at at android.view.View.layout(View.java:15671)
  at at android.view.ViewGroup.layout(ViewGroup.java:5038)
  at at com.android.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:494)
  at at android.view.View.layout(View.java:15671)
  at at android.view.ViewGroup.layout(ViewGroup.java:5038)
  at at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
  at at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
  at at android.view.View.layout(View.java:15671)
  at at android.view.ViewGroup.layout(ViewGroup.java:5038)
  at at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2086)
  at at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1843)
  at at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
  at at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
  at at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
  at at android.view.Choreographer.doCallbacks(Choreographer.java:580)
  at at android.view.Choreographer.doFrame(Choreographer.java:550)
  at at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
  at at android.os.Handler.handleCallback(Handler.java:739)
  at at android.os.Handler.dispatchMessage(Handler.java:95)
  at at android.os.Looper.loop(Looper.java:135)
  at at android.app.ActivityThread.main(ActivityThread.java:5254)
  at ... 4 more

My key is set in manifest & MainActivity contains Xamarin.FormsMaps.Init(this, bundle) in onCreate();

I don't find the error very helpful, has anyong else seen this?