This error only occurs when I set the firbasedatabase rules to true

This error only occurs when I set the firbasedatabase rules to true​

{ “rules”: { “.read”: “auth != true”, “.write”: “auth != true” } }

My application error
java.lang.NullPointerException:

Attempt to invoke virtual method ‘java.lang.String java.lang.Object.toString()’ on a null object reference at

com.krustoon.done. HomeActivity $41.0 nDataChange (HomeActivity.java:1707) at

com.google.firebase.database.Query$1 .onDataChange(com.google.firebase: firebase-database@@19.0.0:179) at

com.google.firebase.database.core.Val ueEventRegistration.fireEvent(com .google.firebase:firebase

-database@@19.0.0:75)

at

com.google.firebase.database.core.vie w.DataEvent.fire(com.google.firebase: firebase-database@@19.0.0:63)

at

com.google.firebase.database.core.vie w.EventRaiser $1.run(com.google firebase:firebase-database@@19.0.0:

at

android.os.Handler.handleCallback(Han dler.java:938) at

android.os.Handler.dispatchMessage(H andler.java:99)

How to solve this error