NullPointerException in java and MySQL

Question

I am writing a login and registration program in java using MySQL.

When I call the register frame from the login frame, the register frame becomes visible but as soon as I click the "register" button after entering information, NullPointerException occurs??

The interesting fact is the NullPointerException doesn't occur if I open the register frame directly.

code is here:

    void register() {
         try {
             String query ="insert into darkwebregister (CodeID,Email,Password,Age) values (?,?,?,?)";
             pst = con.prepareStatement(query);
             pst.setString( 1,idtext.getText());
             pst.setString( 2,emailtext.getText());
             pst.setString( 3,passtext.getText());
             pst.setString( 4,agetext.getText());
             pst.execute();
             JOptionPane.showMessageDialog(null,"YOU ARE REGISTERED SUCESFULLY !!");
             pst.close();
         }catch(SQLException e1) {
             Logger.getLogger(register.class.getName()).log(Level.SEVERE, null, e1);
         }catch(Exception e2) {
            JOptionPane.showMessageDialog(null, e2);

         }
    }

    void createConnection() {
         try {
             Class.forName("com.mysql.cj.jdbc.Driver");
              con = DriverManager.getConnection("jdbc:mysql://localhost:3306/hackersinfo","root","root");
         }catch(Exception ex) {
             JOptionPane.showMessageDialog( null, ex);
         }
    }