Get Data from File

Code:

private String[] thePlayer = new String[999];
        private int[] waterLevel = new int[999];
        private int new_player=0, new_waterlevel=0;
       
        @EventHandler
            public void onPlayerJoin (PlayerJoinEvent e)
            {
                Player aPlayer = e.getPlayer();
                UUID uuid = aPlayer.getUniqueId();
               
                if (!(this.getConfig().get(uuid + ".Name", aPlayer.getName())))
                {
                    // Add to config.yml
                        getConfig().set(uuid + ".Name", aPlayer.getName());
                        getConfig().set(uuid + ".Water Level", 24000);
                        saveConfig();
                        reloadConfig();
                }
                else
                {
                    thePlayer[++new_player] = this.getConfig().getString(uuid + ".Name");
                    waterLevel[++new_waterlevel] = this.getConfig().getInt(uuid + ".Water Level");
                   
                    for (int i=0; i<new_player; i++)
                        if (aPlayer.equals(thePlayer[i]))
                            aPlayer.sendMessage(uuid + "\n" + thePlayer[i] + "\n" + waterLevel);
                }
            }

At this

Code:

if (!(this.getConfig().get(uuid + ".Name", aPlayer.getName())))

i have this error:
The operator ! is undefined for the argument type(s) Object


How can i solve this ?