Update message of exception of missing mapping between fragment class…

… and location string

library/android-mvc/src/main/java/com/shipdream/lib/android/mvc/view/MvcActivity.java

@@ -535,7 +535,7 @@ private void performForwardNav(final NavigationManager.Event2C.OnLocationForward
 
             Class<? extends MvcFragment> fragmentClass = activity.mapNavigationFragment(event.getCurrentValue().getLocationId());
             if (fragmentClass == null) {
-                throw new RuntimeException("Must provide the class type of fragment for location: "
+                throw new RuntimeException("Cannot find fragment class mapped in MvcActivity.mapNavigationFragment(location) for location: "
                         + event.getCurrentValue().getLocationId());
             } else {
                 FragmentTransaction transaction = fm.beginTransaction();