Added missing nullity annotations for the pager adapters (#219)

Author: PaulWoitaschek

conductor-support/src/main/java/com/bluelinelabs/conductor/support/ControllerPagerAdapter.java

@@ -2,6 +2,7 @@
 
 import android.os.Bundle;
 import android.os.Parcelable;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.view.PagerAdapter;
 import android.util.SparseArray;
@@ -34,14 +35,15 @@ public abstract class ControllerPagerAdapter extends PagerAdapter {
     /**
      * Creates a new ControllerPagerAdapter using the passed host.
      */
-    public ControllerPagerAdapter(Controller host, boolean saveControllerState) {
+    public ControllerPagerAdapter(@NonNull Controller host, boolean saveControllerState) {
         this.host = host;
         savesState = saveControllerState;
     }
 
     /**
      * Return the Controller associated with a specified position.
      */
+    @NonNull
     public abstract Controller getItem(int position);
 
     @Override

conductor-support/src/main/java/com/bluelinelabs/conductor/support/RouterPagerAdapter.java

@@ -2,6 +2,7 @@
 
 import android.os.Bundle;
 import android.os.Parcelable;
+import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v4.view.PagerAdapter;
 import android.util.SparseArray;
@@ -28,7 +29,7 @@ public abstract class RouterPagerAdapter extends PagerAdapter {
     /**
      * Creates a new RouterPagerAdapter using the passed host.
      */
-    public RouterPagerAdapter(Controller host) {
+    public RouterPagerAdapter(@NonNull Controller host) {
         this.host = host;
     }
 
@@ -38,7 +39,7 @@ public RouterPagerAdapter(Controller host) {
      * @param router   The router used for the page
      * @param position The page position to be instantiated.
      */
-    public abstract void configureRouter(Router router, int position);
+    public abstract void configureRouter(@NonNull Router router, int position);
 
     @Override
     public Object instantiateItem(ViewGroup container, int position) {

demo/src/main/java/com/bluelinelabs/conductor/demo/controllers/PagerController.java

@@ -30,7 +30,7 @@ public class PagerController extends BaseController {
     public PagerController() {
         pagerAdapter = new RouterPagerAdapter(this) {
             @Override
-            public void configureRouter(Router router, int position) {
+            public void configureRouter(@NonNull Router router, int position) {
                 if (!router.hasRootController()) {
                     Controller page = new ChildController(String.format(Locale.getDefault(), "Child #%d (Swipe to see more)", position), PAGE_COLORS[position], true);
                     router.setRoot(RouterTransaction.with(page));