How to check if a configuration section contains at least one key?

Hi, I want to make a list from my configuration section.

Code:

if (args[0].equalsIgnoreCase("list")) {
                        if (args.length == 1) {
                            FileConfiguration config = null;
                            File file = new File(Main.getPlugin().getDataFolder()+File.separator+"donjons.yml");
                            config = YamlConfiguration.loadConfiguration(file);
                            StringBuilder sb = new StringBuilder();
                           String prefix = "";
                           for(String s : config.getConfigurationSection("donjons").getKeys(false)) {
                               sb.append(prefix);
                               prefix = ", ";
                               sb.append(s);
                           }
                           sender.sendMessage(colorize("&6&l> &7Donjons: " + sb.toString()));
                        } else {
                            sender.sendMessage(colorize("&6&l> &7Usage: /dj list"));
                        }
                    }

The problem is, when there's no key for this configuration section, it returns : "Donjons: " but I want it to return "There's no donjons yet!".
Thank you in advance, I speak french, so Donjon = Dungeon

Got it with try and catch! (NullPointerException)

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

That's a terrible way to do it, never purposely try getting an error, it's best to handle it. A better way would be:

Code:

Set<String> donjons = config.contains("donjons") ? config.getConfigurationSection("donjons").getKeys(false) : null; // Check if the config contains "donjons", if so, get all the keys, if not, return null.
if (donjons != null && !donjons.isEmpty()) { // Check if the donjons Set isn't empty.
    // Do for loop.
} else {
    sb.append("There's no donjons yet!");
}

By the way, you should really instead have a global variable for the configuration, instead of loading it each time someone types the command.