When I run my code this error appears: Cannot invoke "something" because root is null at "something". How to solve this problem?

Question

package de.itdesign.application;

import de.itdesign.application.model.Root;

public class XMLCalculator {

public static void main(String[] args) {

    SAXParser parse = new SAXParser();
    Root root = parse.parser();

    System.out.println("Root " + root.toString());

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.toString()" because "root" is null at de.itdesign.application.XMLCalculator.main

}

}

I think problem is here: package de.itdesign.application;

import de.itdesign.application.model.Data;
import de.itdesign.application.model.Root;
import org.xml.sax.SAXException;
import javax.xml.parsers.*;

import javax.xml.parsers.SAXParserFactory;
import java.io.File;
import java.io.IOException;

public class SAXParser {

    public Root parser(){
        SAXParserFactory factory = SAXParserFactory.newInstance();
        SAXParserHandler handler = new SAXParserHandler();
        javax.xml.parsers.SAXParser parser;

        try{
            parser = factory.newSAXParser();
        }catch(Exception e){
            System.out.println("Open sax parser error " + e.toString());
            return null;
        }

        File file = new File("data.xml");
            try {
                parser.parse(file, handler);
            } catch (SAXException e) {
                System.out.println("Sax parsing error " + e.toString());
                return null;
            } catch (IOException e) {
                System.out.println("IO parsing error " + e.toString());
                return null;
            }


        return null;
    }


}