<NME> WaypointNavigationApp.java
<BEF> package cgeo.geocaching.apps.navi;

import cgeo.geocaching.models.Waypoint;

import android.support.annotation.NonNull;

import android.app.Activity;

/**
 * interface for navigation to a waypoint
 *
 */
interface WaypointNavigationApp {
    void navigate(@NonNull final Activity activity, @NonNull final Waypoint waypoint);

    boolean isEnabled(@NonNull final Waypoint waypoint);
}

<MSG> simplify null handling in app implementations
<DFF> @@ -2,15 +2,17 @@ package cgeo.geocaching.apps.navi;
 
 import cgeo.geocaching.models.Waypoint;
 
-import android.support.annotation.NonNull;
-
 import android.app.Activity;
+import android.support.annotation.NonNull;
 
 /**
  * interface for navigation to a waypoint
  *
  */
 interface WaypointNavigationApp {
+    /**
+     * Navigate to the given waypoint. The caller will assert that waypoint.getCoords() is not null.
+     */
     void navigate(@NonNull final Activity activity, @NonNull final Waypoint waypoint);
 
     boolean isEnabled(@NonNull final Waypoint waypoint);

simplify null handling in app implementations