When checking String == null I get - Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

package com.teamtreehouse;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.Arrays;
import java.util.List;

public class Main {

    public static void main(String[] args) {
        // write your code here
        //String story = "Make me a __placeholder1__ and I'll __placeholder2__ it __placeholder3__ __placeholder4__.";
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String story = null;
        try {
            story = reader.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        Template tmpl = new Template(story);

        Prompter pr = new Prompter();
        pr.run(tmpl);

    }
}

package com.teamtreehouse;

import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;


public class Prompter {
    private BufferedReader mReader;
    private Set<String> mCensoredWords;

    public Prompter() {
        mReader = new BufferedReader(new InputStreamReader(System.in));
        loadCensoredWords();
    }

    private void loadCensoredWords() {
        mCensoredWords = new HashSet<String>();
        Path file = Paths.get("resources", "censored_words.txt");
        List<String> words = null;
        try {
            words = Files.readAllLines(file);
        } catch (IOException e) {
            System.out.println("Couldn't load censored words");
            e.printStackTrace();
        }
        mCensoredWords.addAll(words);
    }

    public void run(Template tmpl) {
        List<String> results = null;
        try {
            results = promptForWords(tmpl);
        } catch (IOException e) {
            System.out.println("There was a problem prompting for words");
            e.printStackTrace();
            System.exit(0);
        }
        String sentence = tmpl.render(results);
//        System.out.printf("Your TreeStory:%n%n%s", sentence);
        System.out.printf("%n%s", sentence);
    }

    /**
     * Prompts user for each of the blanks
     *
     * @param tmpl The compiled template
     * @return
     * @throws IOException
     */
    public List<String> promptForWords(Template tmpl) throws IOException {
        List<String> words = new ArrayList<String>();
        for (String phrase : tmpl.getPlaceHolders()) {
            String word = promptForWord(phrase);
            words.add(word);
        }
        return words;
    }


    /**
     * Prompts the user for the answer to the fill in the blank.  Value is guaranteed to be not in the censored words list.
     *
     * @param phrase The word that the user should be prompted.  eg: adjective, proper noun, name
     * @return What the user responded
     */
    public String promptForWord(String phrase) throws IOException {
        String newWord = "";
        do {
            //System.out.println("Sorry, this word is censored, try again.");
            System.out.printf("%nWrite me one %s: ", phrase);
            newWord = mReader.readLine();
        } while (mCensoredWords.contains(newWord) ||
                 newWord == null);

        return newWord;
    }
}