How to do Firebase query(.equalTo(key))on childListener and map to String

I am doing a details activity so I am passing DatabaseReference FireKey as getExtras and that is working,I want to query the child and map the data,however I am getting an error,

UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
                                                                                at graph.app.com.foodgraph.MealDetailsActivity$1.onChildAdded(MealDetailsActivity.java:130)

This is my code

 mDatabase.addChildEventListener(new ChildEventListener() {
               @Override
               public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                   Intent i = getIntent();
                   final String key = i.getExtras().getString("firekey");

                  System.out.println(dataSnapshot.getRef().equalTo(key) + " value is ");
                   ;

                   Map<String, Object> newPost = (Map<String, Object>) dataSnapshot.getValue();
                   if (newPost != null) {
                       reportSingle = new FoodItem(newPost.get("MEAL_TITLE").toString().trim(),

}