Dúvida no Ex. 3 da Aula 5 - Connection Pool e Datasources

quando tento executar a classe Testa Listagem recebo o erro abaixo: Exception in thread "main" java.lang.NullPointerException at org.hsqldb.DatabaseURL.parseURL(Unknown Source) at org.hsqldb.jdbc.JDBCDriver.getConnection(Unknown Source) at org.hsqldb.jdbc.pool.JDBCPooledDataSource.getPooledConnection(Unknown Source) at org.hsqldb.jdbc.JDBCPool.getConnection(Unknown Source) at br.com.raquelzinha.jdbc.ConnectionPool.getConnection(ConnectionPool.java:27) at br.com.raquelzinha.jdbc.TestaListagem.main(TestaListagem.java:15)

Código:

package br.com.raquelzinha.jdbc;

import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Connection;

public class TestaListagem {


    public static void main(String[] args) throws SQLException{
        ConnectionPool database = new ConnectionPool();

        for(int i = 0; i<100; i++){
            Connection connection = database.getConnection();

            Statement statement = connection.createStatement();
            boolean resultado = statement.execute("select * from Produto");
            ResultSet resultSet = statement.getResultSet();

            while (resultSet.next() == true)
            {
                int id = resultSet.getInt("id");
                String nome = resultSet.getString("nome");
                String descricao = resultSet.getString("descricao");

                System.out.println(id);
                System.out.println(nome);
                System.out.println(descricao);
            }

            resultSet.close();
            statement.close();

            connection.close();
        }
    }




}