Paging library keeps adding data when using pagekeyeddatasource with recycler view. How can I stop it?

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Java

Android

I want to perform pagination and have implemented it . It runs but the exact paages keep repeating themselves.

public class ScheduleDataSource extends PageKeyedDataSource<Long,GeneralMatchItem> {

public void loadInitial (@NonNull LoadInitialParams<Long> params, @NonNull LoadInitialCallback<Long, GeneralMatchItem> callback){


total_items = response_obj.getInt("total_items"); // This is the total items received fromthe response
....
....


callback.onResult(internationalScheduledMatchItemsList,null, 2L);



}



public void loadAfter(@NonNull LoadParams<Long> params, @NonNull LoadCallback<Long, GeneralMatchItem> callback) {


....

long nextKey = (params.key == total_items)? null : params.key+1; //  This throws null pointer when the pages are 12/12

callback.onResult(tempList,nextKey);

}




...
}

What I have tried:

I tried to track the position manually like this mentioned in the code block above:

As i keep srolling then the key gets added till it reaches 12,i.e, 12/12 complete and suddenly i get a null pointer exception

D/ScheduleDataSource: KEY 11AND TOTAL ITEMS :12

I was learning from this tutorial and had implemented most of it. But i can't get rid of this error .

The null pointer i get is :

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.xyz, PID: 5794
    java.lang.NullPointerException: Attempt to invoke virtual method 'long java.lang.Long.longValue()' on a null object reference
        at com.xyz.homescreen_new.utilities.schecdule_util.ScheduleDataSource$2.onResponse(ScheduleDataSource.java:252)
        at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:71)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

I am not able to understand what is going wrong in this. Please help .

TIA . :)