loadPeople.kt

db.collection("Person").get().addOnSuccessListener { query ->
            if (!query.isEmpty) {
                val list = query.documents

                for (d in list) {
                    val person: Person? = d.toObject(Person::class.java)
                  
                    if (person != null) {
                        person.id = d.id
                        mPeople.add(person)
                    }
                }
                mAdapter.notifyDataSetChanged()
     }
}