Fix null string crash

android/java/app/src/main/res/layout/activity_main.xml

@@ -1,11 +1,13 @@
 <merge xmlns:android="http://schemas.android.com/apk/res/android"
-       xmlns:tools="http://schemas.android.com/tools"
-       tools:context="${packageName}.${activityClass}" >
+    xmlns:tools="http://schemas.android.com/tools"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    tools:context="${packageName}.${activityClass}">
 
     <view
         android:layout_width="fill_parent"
         android:layout_height="fill_parent"
         class="com.mapbox.mapboxgl.lib.MapView"
-        android:id="@+id/map" />
+        android:id="@+id/map"
+        app:styleUrl="asset://styles/styles/bright-v6.json"/>
 
 </merge>

android/java/lib/src/main/java/com/mapbox/mapboxgl/lib/MapView.java

@@ -86,7 +86,7 @@ public class MapView extends SurfaceView {
     private boolean mZoomEnabled = true;
     private boolean mScrollEnabled = true;
     private boolean mRotateEnabled = true;
-    private String mStyleUrl = "asset://styles/styles/bright-v6.json";
+    private String mStyleUrl;
 
     //
     // Constructors
@@ -137,7 +137,6 @@ public class MapView extends SurfaceView {
 
         // Create the NativeMapView
         mNativeMapView = new NativeMapView(this, cachePath, dataPath, apkPath);
-        mNativeMapView.setStyleUrl(mStyleUrl);
 
         // Load the attributes
         TypedArray typedArray = context.obtainStyledAttributes(attrs,
@@ -164,8 +163,6 @@ public class MapView extends SurfaceView {
                     R.styleable.MapView_debugActive, false));
             setStyleUrl(typedArray.getString(
                     R.styleable.MapView_styleUrl));
-            setAccessToken(typedArray.getString(
-                    R.styleable.MapView_accessToken));
         } finally {
             typedArray.recycle();
         }

android/java/lib/src/main/res/values/attrs.xml

@@ -8,7 +8,6 @@
     <attr name="rotateEnabled" format="boolean" />
     <attr name="debugActive" format="boolean" />
     <attr name="styleUrl" format="string" />
-    <attr name="accessToken" format="string" />
     
     <declare-styleable name="MapView">
         <attr name="centerLongitude" />
@@ -20,6 +19,5 @@
         <attr name="rotateEnabled" />
         <attr name="debugActive" />
         <attr name="styleUrl" />
-        <attr name="accessToken" />
     </declare-styleable>
 </resources>