Solved I need help on developing a minecraft plugin

I'm developing a ranks plugin, when I run a specified command this is the output:



This is the code of this command:

Code:

import net.milkbowl.vault.economy.Economy;
import net.milkbowl.vault.economy.EconomyResponse;

private static Economy econ;


if(cmd.getName().equalsIgnoreCase("rankup")) {
              
                UUID SenderID = ((Player) sender).getPlayer().getUniqueId();
                String Rank = Main.getPlayersData().getString("Players."+SenderID);
                boolean RankupwithoutspecifyTrack = Boolean.parseBoolean(Main.getConf().getString("Settings.RankupwithoutspecifyTrack"));
                String PlayerName = sender.getName();
                double balance;
                if(args.length == 0) {
              
                    if (RankupwithoutspecifyTrack = true) {
                      
                        String DefaultTrack = Main.getConf().getString("Settings.DefaultTrack");
                        int posintrack = Main.getConf().getInt("Rankslist."+Rank+".positionintrack"+DefaultTrack);
                        int rankuprank = posintrack + 1;
                        String NewRank = Main.getTracksConf().getString("Tracks."+DefaultTrack+"."+rankuprank);
                        pdata.set("Players."+SenderID, NewRank);
                        String RankName = NewRank;
                        sender.sendMessage(""+(econ.getBalance(PlayerName)));
                        double Cost = Main.getConf().getDouble("Rankslist."+RankName+".cost");
                      
                            if((econ.getBalance(PlayerName) - Cost)<= 0) {
                              
                                try {
                                    pdata.save(PlayerData);
                                } catch (IOException e) {
                                    e.printStackTrace();
                                }
                              
                                econ.withdrawPlayer(PlayerName, Cost);
                                sender.sendMessage("§aYou ranked up to "+NewRank+"!");
                            }else {
                                sender.sendMessage("§cYou don't have enough money!");
                              
                            }
                    }else {
                        sender.sendMessage("§cSorry you have to specify track!");
                      
                    }

For Eclipse there isn't any syntax error.
I sent you only the part of command, without others codes.

 

@Calamandrey What is line 356 of your 'Comandi' class?

 

Oh I forgot to give line's numbers.
Line 356 is:
sender.sendMessage(""+(econ.getBalance(PlayerName)));

 

I understood it, but how can I solve it?

 

Nope, that's the first plugin that I code, so I'm not too expert about java coding...
At the head of the class I wrote this:
private static Economy econ;
Isn't it enough?