Android studio is forced to shut down 'java.lang.Stringjava.lang.Object.toString()' on a null object reference

06-20 16:55:53.125 15979-15979/com.ossw.taxiapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.ossw.taxiapp, PID: 15979
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
        at com.ossw.taxiapp.CustomerMapActivity$6.onDataChange(CustomerMapActivity.java:289)
        at com.google.firebase.database.Query$1.onDataChange(com.google.firebase:firebase-database@@19.3.0:179)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.3.0:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.3.0:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.3.0:55)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

    private void getDriverInfo() {
        mDriverInfo.setVisibility(View.VISIBLE);
        DatabaseReference mCustomerDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child("Drivers").child(driverFoundID);
        mCustomerDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists() && dataSnapshot.getChildrenCount() > 0) {
                    if (dataSnapshot.child("name") != null) {
                        d_name.setText(dataSnapshot.child("name").getValue().toString());
                    }
                    if (dataSnapshot.child("phone") != null) {
                        d_phone.setText(dataSnapshot.child("phone").getValue().toString());
                    }
                    if (dataSnapshot.child("car") != null) {
                        d_car.setText(dataSnapshot.child("car").getValue().toString());
                    }
                    if (dataSnapshot.child("carNum") != null) {
                        d_callNum.setText(dataSnapshot.child("callNum").getValue().toString());
                    }
                    if (dataSnapshot.child("profileImageUrl").getValue() != null) {
                        Glide.with(getApplication()).load(dataSnapshot.child("profileImageUrl").getValue().toString()).into(d_profileimg);
                    }

                    int ratingSum = 0;
                    float ratingsTotal = 0;
                    float ratingsAvg = 0;
                    for (DataSnapshot child : dataSnapshot.child("rating").getChildren()) {
                        ratingSum = ratingSum + Integer.valueOf(child.getValue().toString());
                        ratingsTotal++;
                    }
                    if (ratingsTotal != 0) {
                        ratingsAvg = ratingSum / ratingsTotal;
                        mRatingBar.setRating(ratingsAvg);
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });
    }