Exception: JNI:

Any help here?

 Exception: JNI: Init'd AndroidJavaClass with null ptr!
 UnityEngine.AndroidJavaClass..ctor (IntPtr jclass) (at C:/buildslave/unity/build/Runtime/Export/AndroidJavaImpl.cs:556)
 UnityEngine.AndroidJavaObject.get_JavaLangClass () (at C:/buildslave/unity/build/Runtime/Export/AndroidJavaImpl.cs:534)
 UnityEngine.AndroidJavaObject.FindClass (System.String name) (at C:/buildslave/unity/build/Runtime/Export/AndroidJavaImpl.cs:525)
 UnityEngine.AndroidJavaClass._AndroidJavaClass (System.String className) (at C:/buildslave/unity/build/Runtime/Export/AndroidJavaImpl.cs:545)
 UnityEngine.AndroidJavaClass..ctor (System.String className) (at C:/buildslave/unity/build/artifacts/generated/common/runtime/AndroidJavaBindings.gen.cs:94)
 GameManager.IsPlayServicesAvailable () (at Assets/Scripts/General/GameManager.cs:81)
 GameManager.Awake () (at Assets/Scripts/General/GameManager.cs:51)
 

my code

 public bool IsPlayServicesAvailable()
     {
         const string GoogleApiAvailability_Classname =
             "com.google.android.gms.common.GoogleApiAvailability";
         AndroidJavaClass clazz =
             new AndroidJavaClass(GoogleApiAvailability_Classname);
         AndroidJavaObject obj =
             clazz.CallStatic<AndroidJavaObject>("getInstance");
 
         var androidJC = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
         var activity = androidJC.GetStatic<AndroidJavaObject>("currentActivity");
 
         int value = obj.Call<int>("isGooglePlayServicesAvailable", activity);
 
         // 0 == success
         // 1 == service_missing
         // 2 == update service required
         // 3 == service disabled
         // 18 == service updating
         // 9 == service invalid
         return value == 0;
     }