Only valid managed objects can be copied from Realm - Android

04-20 11:40:01.766 464-464/quizcounter.geeks.compete.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
    Process: quizcounter.geeks.compete.myapplication, PID: 464
java.lang.IllegalArgumentException: Only valid managed objects can be copied from Realm.
        at io.realm.Realm.checkValidObjectForDetach(Realm.java:1745)
        at io.realm.Realm.copyFromRealm(Realm.java:1418)
        at io.realm.Realm.copyFromRealm(Realm.java:1391)
        at quizcounter.geeks.compete.myapplication.SplashScreenActivity$setAllPaperDataToDB$1.onDataChange(SplashScreenActivity.java:546)
        at com.google.firebase.database.Query$1.onDataChange(com.google.firebase:firebase-database@@16.1.0:183)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@16.1.0:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@16.1.0:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@16.1.0:55)
        at android.os.Handler.handleCallback(Handler.java:742)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:157)
        at android.app.ActivityThread.main(ActivityThread.java:5603)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:774)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)