FATAL EXCEPTION: main (Ask Gemini)
                                                                                                    Process: com.example.memorygameone, PID: 4904
                                                                                                    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.memorygameone/com.example.memorygameone.NicknameActivity}: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.example.memorygameone. Make sure to call FirebaseApp.initializeApp(Context) first.
                                                                                                    	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3308)
                                                                                                    	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3457)
                                                                                                    	at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
                                                                                                    	at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
                                                                                                    	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
                                                                                                    	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2044)
                                                                                                    	at android.os.Handler.dispatchMessage(Handler.java:107)
                                                                                                    	at android.os.Looper.loop(Looper.java:223)
                                                                                                    	at android.app.ActivityThread.main(ActivityThread.java:7562)
                                                                                                    	at java.lang.reflect.Method.invoke(Native Method)
                                                                                                    	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
                                                                                                    	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
                                                                                                    Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.example.memorygameone. Make sure to call FirebaseApp.initializeApp(Context) first.
                                                                                                    	at com.google.firebase.FirebaseApp.getInstance(FirebaseApp.java:179)
                                                                                                    	at com.google.firebase.database.FirebaseDatabase.getInstance(FirebaseDatabase.java:56)
                                                                                                    	at com.example.memorygameone.DB.<init>(DB.java:40)
                                                                                                    	at com.example.memorygameone.NicknameActivity.onCreate(NicknameActivity.java:23)
                                                                                                    	at android.app.Activity.performCreate(Activity.java:7906)
                                                                                                    	at android.app.Activity.performCreate(Activity.java:7893)
                                                                                                    	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
                                                                                                    	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3283)
                                                                                                    	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3457) 
                                                                                                    	at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
                                                                                                    	at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
                                                                                                    	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
                                                                                                    	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2044) 
                                                                                                    	at android.os.Handler.dispatchMessage(Handler.java:107) 
                                                                                                    	at android.os.Looper.loop(Looper.java:223) 
                                                                                                    	at android.app.ActivityThread.main(ActivityThread.java:7562) 
                                                                                                    	at java.lang.reflect.Method.invoke(Native Method) 
                                                                                                    	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539) 
                                                                                                    	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950) 


что не так?