java.sql.SQLException: Connection is closed [POOL-HikariCP]

Hello i have a problem with the connection, it is closing the connection while performing a Query. I don´t know what happens D: Here is the configuration:

private static HikariDataSource Hikari;
public static String ID_Usuario;

public void connectToDatabase() {       

    Hikari = new HikariDataSource();       
    Hikari.setDriverClassName("com.mysql.jdbc.Driver");
    Hikari.setJdbcUrl("jdbc:mysql://localhost:3306/bank");
    Hikari.setUsername("root");
    Hikari.setPassword(""); 
    Hikari.setMaximumPoolSize(5);
    Hikari.setConnectionTimeout(300000);
    Hikari.addDataSourceProperty("cachePrepStmts", "true");
    Hikari.addDataSourceProperty("prepStmtCacheSize", "250");
    Hikari.addDataSourceProperty("prepStmtCacheSqlLimit", "2048");
    Hikari.setConnectionTestQuery("SELECT 1");
}

public HikariDataSource getHikari(){
    return Hikari;
}

Now, here is the class where i used the pool, First i recieved a connection from Hikari.getConnection(). Then i saved it in "connection"

Pool HikariPool;
HikariDataSource Hikari;
Connection connection;

  public SQL() {
    initComponents();
  }

    public void initComponents(){
        HikariPool= new Pool();
        HikariPool.connectToDatabase();

    Hikari=HikariPool.getHikari();

    try{
       connection= Hikari.getConnection();
    }catch(SQLException e){
        e.printStackTrace();
    }
}

And i use the "connection" in validateLogin()

public int validateLogin(String nip){
   int validation=0;
   String SQL="SELECT * FROM bank.account WHERE No_Account='"+account+"'   
    AND NIP='"+nip+"'";
    try{
        Statement stm=Conexion.createStatement();
        ResultSet rs= stm.executeQuery(SQL);
...

At line " Statement stm=connection.createStatement();" an error ocurred

it says :

[AWT-EventQueue-0] INFO com.zaxxer.hikari.HikariDataSource - HikariPool-0  
- is starting.
java.sql.SQLException: Connection is closed at   
com.zaxxer.hikari.pool.ProxyConnection$ClosedConnection$1.invoke
(ProxyConnection.java:468)
at com.sun.proxy.$Proxy0.createStatement(Unknown Source)...

Why is closing the connection?