group values of list of key values pairs

Grouper.java

import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.AbstractMap.SimpleEntry;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Grouper {

    public static void main(String[] args) {
        if(args == null || args.length == 0) {
            System.out.println("Usage: java -cp <your-java-cp> Grouper file.csv");
            System.exit(0);
        }

        try (Stream<String> lines = Files.lines(Paths.get(args[0]))) {
            lines.map(l -> l.split(","))
                    .map(l -> new SimpleEntry<>(l[0], Double.parseDouble(l[1])))
                    .collect(Collectors.groupingBy(SimpleEntry::getKey,
                            Collectors.averagingDouble(SimpleEntry::getValue)))
                    .entrySet()
                    .stream()
                        .map(e -> e.getKey() + "=" + String.format("%.4f", e.getValue()))
                        .forEach(System.out::println);
        } catch (Exception e) {
            System.out.println("An error occurred! " + e.getMessage());
            System.out.println("Please make sure your key/value pairs have the following format: /my/string,13.37");
        }
    }
}

I've got a NPE in line 11. Why?? Plesse advice

http://stackoverflow.com/a/3868882/789738