Android DatabaseException Error when retrieving data

I am attempting to learn how to implement Firebase into an existing project that previously used a SQL db. I have the write code working correctly, but my read is throwing the DatabaseException error below.

com.google.firebase.database.DatabaseException: Found a conflicting setters with name: setWallpaper (conflicts with setWallpaper defined on android.content.ContextWrapper)

I have done a good bit of research and can only find references to this error when writing to the database, not reading from it, so I am very much confused as to what I might have done in my code to cause this error to happen. The method code is below.

protected void lastFive() {
    final DatabaseReference gameRef = database.getReference("Games");
    final List<User> gamesList = new ArrayList<>();
    gameRef.orderByChild("Date").limitToLast(5).addValueEventListener (new ValueEventListener ( ) {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            gamesList.clear ();
            for (DataSnapshot postSnapshot: dataSnapshot.getChildren ()){
                User user = postSnapshot.getValue(User.class);
                gamesList.add (user);
                System.out.println(user.getName () + " : " + user.getScore ());
            }
        }

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

The line in the method the error appears to be referencing is:

User user = postSnapshot.getValue(User.class);

I have only been working in Android for a couple months off and on, and Firebase less than half that, so it is possible there is some glaring error in this I simply do not see. FWIW, this method is intended to display the username and score for the last 5 games played on the app. I am a bit concerned what the output will look like, which I know is outside the scope of this question, but I am unable to even work on that until I can read the data. Any help or suggestion is greatly appreciated.

User code being added as requested.

public class User extends Application {

    //private variable
    private static User globalVar;

    //variables
    String _id;
    String _name;
    int _score;
    String _date;
    String _email;

    // Empty constructor
    public User(){}

    // constructor
    public User(String id, String name, int score, String date){
        this._id = id;
        this._name = name;
        this._score = score;
        this._date = date;
    }

    public User(String id, int score){
        this._id = id;
        this._score = score;
    }

    public User(String id){
        this._id = id;
    }

    public User(int score, String date){
        this._score = score;
    }

    // getting ID
    public String getID(){
        return this._id;
    }

    // setting id
    public void setID(String id){
        this._id = id;
    }

    // getting name
    public String getName(){
        return this._name;
    }

    // setting name
    public void setName(String name){
        this._name = name;
    }

    // getting scores
    public int getScore(){ return this._score; }

    // setting scores
    public void setScore(int score){ this._score = score; }

    // getting name
    public String getDate(){
        return this._date;
    }

    // setting name
    public void setDate(String date){
        this._date = date;
    }

    // getting email
    public String getEmail(){
        return this._email;
    }

    // setting email
    public void setEmail(String email){
        this._email = email;
    }

    public static synchronized User getGlobalVar(){
        if(globalVar == null){
            globalVar = new User();
        }
        return globalVar;
    }
}