Hmm FunFacts Stopped Working Error

package com.stucowley.funfacts;

import android.content.DialogInterface;
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.widget.TextView;

import java.util.Random;

public class FunFactsActivity extends AppCompatActivity {
    private FactBook mFactBook = new FactBook();

    // Declare our view variables
    private TextView mFactTextView;
    private Button mShowFactButton;
    private RelativeLayout mRelativeLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fun_facts);

        // Assign the Views from the layout file to the corresponding variables
        mFactTextView = (TextView) findViewById(R.id.factTextView);
        mShowFactButton = (Button) findViewById(R.id.showFactButton);
        mRelativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout);

        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String fact = mFactBook.getFact();

                // Update the screen with our dynamic fact
                mFactTextView.setText(fact);
                mRelativeLayout.setBackgroundColor(Color.RED);
            }
        };
        mShowFactButton.setOnClickListener(listener);

    }
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="50dp"
    android:paddingLeft="50dp"
    android:paddingRight="50dp"
    android:paddingTop="50dp"
    android:id="@+id/relativeLayout"
    android:background="#51b46d"
    tools:context="com.stucowley.funfacts.FunFactsActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Did you know?"
        android:textColor="#80ffffff"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.062"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.03"
        tools:text="Did you know?"
        android:id="@+id/textView"/>

    <TextView
        android:id="@+id/factTextView"
        android:layout_width="0dp"
        android:layout_height="186dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:text="Ants stretch when they wake up in the morning."
        android:gravity="center_vertical"
        android:textColor="@android:color/white"
        android:textSize="24sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        tools:layout_constraintLeft_creator="1"
        tools:layout_constraintRight_creator="1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_constraintTop_creator="1"
        tools:layout_constraintBottom_creator="1"/>

    <Button
        android:id="@+id/showFactButton"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:background="@android:color/white"
        android:text="Show Another Fun Fact"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        tools:layout_constraintBottom_creator="1"
        tools:layout_constraintLeft_creator="1"
        tools:layout_constraintRight_creator="1" />

</android.support.constraint.ConstraintLayout>