Null pointer error...

// Member variable (properties about the object)
public String[] mFacts = {
        "Ants stretch when they wake up in the morning.",
        "Ostriches can run faster than horses.",
        "Olympic gold medals are actually made mostly of silver.",
        "You are born with 300 bones; by the time you are an adult you will have 206.",
        "It takes about 8 minutes for light from the Sun to reach Earth.",
        "Some bamboo plants can grow almost a meter in just one day.",
        "The state of Florida is bigger than England.",
        "Some penguins can leap 2-3 meters out of the water.",
        "On average, it takes 66 days to form a new habit.",
        "Mammoths still walked the earth when the Great Pyramid was being built.",
        "Treehouse is not actually in a tree."};
// Method (abilities: these are things the object can do)

public String getFact(){ 

// Here you created a method, However you are already in a method which is the onClick method
// You cannot create a method within a method.
// delete the method but leave the following code. Dont forget to delete its closing curly brace.

    String fact = "";
    // Randomly select a fact
    Random randomGenerator = new Random(); //Construct a new Random number generator
   //Create a variable to store an int that will be used to hold a position in my mFacts Array object.
    int randomNumber = randomGenerator.nextInt(mFacts.length); // Grab a value and store it in our int variable.
    //fact is being made equal to randomNumber adding an empty
    fact = randomNumber + ""; // You do not need this. Look at your statement after this one.
    fact = mFacts[randomNumber]; 

/* This statement above allows you to get string from the array you created. Lets break it down.
 *  You created a String variable named Facts to store a string.
 *  You also created an Array object called mFacts which holds numerous Strings. 
 *  Now you must get a position in the array to grab a hold of one of the strings.
 * This is where the randomNumber variable comes into play.
 * instead of assigning the 11 strings to a variable such as 
 * String stringOne = mFacts[0];
 * String stringTwo = mFacts[1];
 * You are instead saying i want to use a string in my array mFacts but i want it to be random. 
 * So use the integer stored in randomNumber and assign it a position inside my array mFacts.
 * Store this string inside fact.
*/

    return fact; // Since our method  onClick() has a state of void it does not need to return a value. Delete it.
}

package com.arkman.funfacts;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.Random;


public class FunFactsActivity extends Activity {

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

        //Declare our view variables and assign them the views from the layout files
        final TextView factLabel = (TextView) findViewById(R.id.factTextView);
        Button showFactButton = (Button) findViewById(R.id.showFactButton);

        View.OnClickListener listener = new View.OnClickListener() {

            public void onClick(View view) {
                String[] mFacts = {
                        "Ants stretch when they wake up in the morning.",
                        "Ostriches can run faster than horses.",
                        "Olympic gold medals are actually made mostly of silver.",
                        "You are born with 300 bones; by the time you are an adult you will have 206.",
                        "It takes about 8 minutes for light from the Sun to reach Earth.",
                        "Some bamboo plants can grow almost a meter in just one day.",
                        "The state of Florida is bigger than England.",
                        "Some penguins can leap 2-3 meters out of the water.",
                        "On average, it takes 66 days to form a new habit.",
                        "Mammoths still walked the earth when the Great Pyramid was being built." }; // my list of facts held in an Array object

                //randomly select a fact

                Random randomGenerator = new Random(); // create a reference variable to store the Random class
                int randomNumber = randomGenerator.nextInt(mFacts.length); // Create a variable that will be used to store a random int

                String fact = ""; // Create a variable that will be used to store a String from my array object named mFacts
                fact = mFacts[randomNumber]; // Use the integer stored in randomNumber to hold a position inside my Array Object

                //Update the label with our dynamic fact

                factLabel.setText(fact); // set my TextView object called factLabel to the String stored in fact

            }
        };
        showFactButton.setOnClickListener(listener); // wait for my Button to be pressed. Then update using the onClick method.

    }

    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_fun_facts, menu);
        return true;
    }

    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}