NullPointerException when I tried to context.write function

Question

My problem is Nullpointer, and I spent a whole day but end up finding nothing.

Here is my basic class

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import java.util.HashMap;
import java.util.Map;

class User implements Writable {
    private String UserID;
    private String Gender;
    private String age;
    private String Occupation;
    private String Zip_code;

    public static final Map<String, String> GenderMap = new HashMap() {
        {
            put("F", "Female");
            put("M", "Male");
        }
    };
    public static final Map<String, String> AgeMap = new HashMap() {
        {
            put("1", "Under 18");
            put("18", "18-24");
            put("25", "25-34");
            put("35", "35-44");
            put("45", "45-49");
            put("50", "50-55");
            put("56", "56+");
        }
    };
    public static final Map<String, String> OcupMap = new HashMap() {
        {
            put("  0", "othe");
            put("  1", "academic/educato");
            put("  2", "artis");
            put("  3", "clerical/admi");
            put("  4", "college/grad stude");
            put("  5", "customer servic");
            put("  6", "doctor/health car");
            put("  7", "executive/manageria");
            put("  8", "farme");
            put("  9", "homemake");
            put(" 10", "K-12 studen");
            put(" 11", "lawye");
            put(" 12", "programme");
            put(" 13", "retire");
            put(" 14", "sales/marketin");
            put(" 15", "scientis");
            put(" 16", "self-employe");
            put(" 17", "technician/enginee");
            put(" 18", "tradesman/craftsma");
            put(" 19", "unemploye");
            put(" 20", "write");
        }
    };

    public User() {
    }

    public User(String userID) {
        UserID = userID;
    }

    public User(String userID, String gender, String age, String occupation, String zip_code) {
        UserID = userID;
        Gender = gender;
        this.age = age;
        Occupation = occupation;
        Zip_code = zip_code;
    }

    public String getUserID() {
        return UserID;
    }

    public void setUserID(String userID) {
        UserID = userID;
    }

    public void setRest(User a) {
        this.Gender = a.Gender;
        this.age = a.age;
        this.Occupation = a.Occupation;
        this.Zip_code = a.Zip_code;
    }

    @Override
    public void write(DataOutput dataOutput) throws IOException {
        dataOutput.writeUTF(UserID);
        dataOutput.writeUTF(Gender);
        dataOutput.writeUTF(age);
        dataOutput.writeUTF(Occupation);
        dataOutput.writeUTF(Zip_code);
    }

    @Override
    public void readFields(DataInput dataInput) throws IOException {
        UserID = dataInput.readUTF();
        Gender = dataInput.readUTF();
        age = dataInput.readUTF();
        Occupation = dataInput.readUTF();
        Zip_code = dataInput.readUTF();
    }

    @Override
    public String toString() {
        return "UserID=" + UserID +
                ", Gender='" + Gender + '\'' +
                ", age='" + age + '\'' +
                ", Occupation='" + Occupation + '\'' +
                ", Zip_code='" + Zip_code + "\',";

    }

}

class Movie implements Writable {
    private String MovieID;
    private String Title;
    private String Genres;

    public Movie() {
    }

    public Movie(String movieID) {
        MovieID = movieID;
    }

    public Movie(String movieID, String title, String genres) {
        MovieID = movieID;
        Title = title;
        Genres = genres;
    }

    public void setRest(Movie a) {
        Title = a.Title;
        Genres = a.Genres;
    }

    public String getMovieID() {
        return MovieID;
    }

    public void setMovieID(String movieID) {
        MovieID = movieID;
    }

    @Override
    public void write(DataOutput dataOutput) throws IOException {
        dataOutput.writeUTF(MovieID);
        dataOutput.writeUTF(Title);
        dataOutput.writeUTF(Genres);
    }

    @Override
    public void readFields(DataInput dataInput) throws IOException {
        MovieID = dataInput.readUTF();
        Title = dataInput.readUTF();
        Genres = dataInput.readUTF();
    }

    @Override
    public String toString() {
        return "MovieID=" + MovieID +
                ", Title='" + Title + '\'' +
                ", Genres='" + Genres + '\'';

    }
}

class Rate implements WritableComparable<Rate> {
    private User user = new User();
    private Movie movie = new Movie();
    private String rate;
    private String timestamp;

    public Rate() {
    }

    public Rate(String userid, String movieid, String rate, String timestamp) {
        user.setUserID(userid);
        movie.setMovieID(movieid);
        this.rate = rate;
        this.timestamp = timestamp;
    }

    @Override
    public void write(DataOutput dataOutput) throws IOException {
        user.write(dataOutput);
        movie.write(dataOutput);
        dataOutput.writeUTF(rate);
        dataOutput.writeUTF(timestamp);
    }

    @Override
    public void readFields(DataInput dataInput) throws IOException {
        user.readFields(dataInput);
        movie.readFields(dataInput);
        timestamp = dataInput.readUTF();
    }

    @Override
    public String toString() {
        return "Rate{" + user + movie +
                ", rate=" + rate +
                ", timestamp='" + timestamp + '\'' +
                '}';
    }

    public User getUser() {
        return user;
    }

    public Movie getMovie() {
        return movie;
    }

    @Override
    public int compareTo(Rate o) {
        return 0;
    }
} 

Here is my main class

public class Homework2 {
    private static Map<String, User> users = new HashMap<>();
    private static Map<String, Movie> movies = new HashMap<>();

    public static class GenderMapper extends Mapper<LongWritable, Text, Rate, NullWritable> {
        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String s = value.toString();
            String[] fields = s.split("::");
            if (fields.length == 3) {
                movies.put(fields[0], new Movie(fields[0], fields[1], fields[2]));
            } else if (fields.length == 4) {
                Rate rate = new Rate(fields[0], fields[1], fields[2], fields[3]);
                System.out.println(rate);
                context.write(rate, null);
            } else if (fields.length == 5) {
                users.put(fields[0], new User(fields[0],
                                User.GenderMap.get(fields[1]),
                                User.AgeMap.get(fields[2]),
                                User.OcupMap.get(fields[3]),
                                fields[4])
                );
            }
        }
    }

    public static class GenderReducer extends Reducer<Rate, NullWritable, Rate, NullWritable> {
        @Override
        protected void reduce(Rate key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {
            String userId = key.getUser().getUserID();
            String movieId = key.getMovie().getMovieID();
            key.getUser().setRest(users.get(userId));
            key.getMovie().setRest(movies.get(movieId));
            context.write(key, null);
        }
    }


    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        Configuration conf = new Configuration();
        GenericOptionsParser optionsParser =
                new GenericOptionsParser(conf, args);

        String[] remainingArgs = optionsParser.getRemainingArgs();
        if (remainingArgs.length < 2) {
            System.out.println("Usage: MRJobname <in> [<in>...] , <out>");
            System.exit(2);
        }
        Job job = Job.getInstance(conf);
        job.setJobName("Homework2");
        job.setJarByClass(Homework2.class);

   
        for (int i = 0; i < remainingArgs.length - 1; i++) {
            FileInputFormat.addInputPath(
                    job, new Path(remainingArgs[i]));
        }
        job.setInputFormatClass(TextInputFormat.class);
        job.setMapperClass(GenderMapper.class);
        job.setMapOutputKeyClass(Rate.class);
        job.setMapOutputValueClass(NullWritable.class);

        
        job.setNumReduceTasks(1);   // 1, 0
        job.setReducerClass(GenderReducer.class);
        job.setOutputKeyClass(Rate.class);
        job.setOutputValueClass(NullWritable.class);

        
        FileOutputFormat.setOutputPath(job,
                new Path(remainingArgs[remainingArgs.length - 1]));
        job.setOutputFormatClass(TextOutputFormat.class);

        job.waitForCompletion(true);
        boolean result = job.isSuccessful();
        System.exit(result ? 0 : 1);
    }
}

my input text is like this

movie.txt 

1::Toy Story (1995)::Animation|Children's|Comedy
2::Jumanji (1995)::Adventure|Children's|Fantasy
3::Grumpier Old Men (1995)::Comedy|Romance
4::Waiting to Exhale (1995)::Comedy|Drama
5::Father of the Bride Part II (1995)::Comedy
6::Heat (1995)::Action|Crime|Thriller
7::Sabrina (1995)::Comedy|Romance
8::Tom and Huck (1995)::Adventure|Children's
9::Sudden Death (1995)::Action
10::GoldenEye (1995)::Action|Adventure|Thriller
11::American President, The (1995)::Comedy|Drama|Romance
12::Dracula: Dead and Loving It (1995)::Comedy|Horror
13::Balto (1995)::Animation|Children's
14::Nixon (1995)::Drama
15::Cutthroat Island (1995)::Action|Adventure|Romance
16::Casino (1995)::Drama|Thriller
17::Sense and Sensibility (1995)::Drama|Romance
18::Four Rooms (1995)::Thriller
19::Ace Ventura: When Nature Calls (1995)::Comedy

user.txt

1::F::1::10::48067
2::M::56::16::70072
3::M::25::15::55117
4::M::45::7::02460
5::M::25::20::55455
6::F::50::9::55117
7::M::35::1::06810
8::M::25::12::11413
9::M::25::17::61614
10::F::35::1::95370
11::F::25::1::04093
12::M::25::12::32793
13::M::45::1::93304
14::M::35::0::60126
15::M::25::7::22903
16::F::35::0::20670
17::M::50::1::95350
18::F::18::3::95825

rating.txt
1::1193::5::978300760
1::661::3::978302109
1::914::3::978301968
1::3408::4::978300275
1::2355::5::978824291
1::1197::3::978302268
1::1287::5::978302039
1::2804::5::978300719
1::594::4::978302268
1::919::4::978301368
1::595::5::978824268
1::938::4::978301752
1::2398::4::978302281
1::2918::4::978302124
1::1035::5::978301753
1::2791::4::978302188

and each number stands for each different job. that's why I use HashMap to handle them.

I really appreciate what you help me solve this problem.

Thank you guys again. Wish you have a good future