'java.lang.NumberFormatException: For input string: "null"'.

Hello, i working on my plugin ( connect with website messages )

Code:

if (prikaz.getName().equalsIgnoreCase("zprava"))
                        {
                            if(hrac.hasPermission("freelance.prikaz.zprava"))
                                {
                                    if (args.length == 0)
                                    {
                                        hrac.sendMessage(zluta + "/zprava archiv " + bila + "Zobrazíte historii zpráv.");
                                        hrac.sendMessage(zluta + "/zprava hráč text " + bila + "Pošlete soukromou zprávu hráči.");
                                    }
                                    String text = "";
                                    Calendar cal = Calendar.getInstance();
                                    SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
                                    for (int i = 1; i < args.length; i++) text += (i > 1 ? " " : "") + args[i];
                                    Player target = Bukkit.getPlayer(args[0]);
                                    if (target != null)
                                    {
                                        if (args.length >= 2)
                                        {
                                            odesilatel.sendMessage(svetleseda + "[" + zelena + "Zpráva" + bila + " -> " + target.getName() + svetleseda + "]: " + zluta + text); // Co se ukáže mě
                                            target.sendMessage(svetleseda + "[" + hrac.getName() + bila + " - > " + zelena + "Zpráva" + svetleseda + "]: " + zluta + text); // Co se ukáže tomu na druhé straně
                                            try {
                                                    mysql2.open();
                                                    mysql2.query("SELECT user_id FROM fusion95V14_users WHERE user_name = '" + hrac.getName() + "' OR user_name = '" + target.getName() + "'");
                                                    mysql2.query("INSERT INTO fusion95V14_messages (message_from, message_to, message_message, message_datestamp) VALUES (user_id, user_id, '" + text + "', '" + sdf.format(cal.getTime()) + "')");
                                                } catch (SQLException e) {
                                                e.printStackTrace();
                                                }
                                              return true;       
                                        } else {
                                            odesilatel.sendMessage(cervena + "Špatné zadání, použíjte " + zelena + "/zprava (hráč) (text)");
                                        }
                                    } else {
                                        hrac.sendMessage("Osoba " + args[0] + " neexistuje, nebo je offline.");
                                    }
                                } else {
                                    hrac.sendMessage(cervena + "Nemáš oprávnění!");
                                }
                            if (args.length == 1)
                            {
                                if (args[0].equalsIgnoreCase("archiv"))
                                {
                                    if(hrac.hasPermission("freelance.prikaz.zprava.archiv"))
                                    {
                                            //try {
                                                //mysql.open();
                                                //ResultSet Query = mysql.query("SELECT * FROM FreeLance_ZPRAVA WHERE hrac LIKE '" + hrac.getName() + "' LIMIT 10");
                                                //if(Query.next())
                                                //{
                                                //    hrac.sendMessage(Query.getString("hrac" + "dorucovatel" + "obsah"));
                                                //}
                                            //} catch (SQLException e) {
                                                //e.printStackTrace();
                                            //}
                                            return true;
                                    } else {
                                        hrac.sendMessage(cervena + "Nemáš oprávnění!");
                                    }
                                } else {
 
                                }
                            }
                        }

Error Log:
http://pastebin.com/BKb2LJ1J
at freelance.plugin.by.sionzee.all.in.one.FreeLance.onCommand(FreeLance.java:455)
is:
mysql2.open();


What is bad ?

 

Are you constructing your MySQL class properly? It seems that the NFE is coming from something above this class