Solved Read prefix from config

Hi, I need help.
I need to read the prefix entered by the user from the config.

I tried this code:

Code:

public FileConfiguration cfg = this.getLang();
public String prefix = cfg.getString("JoinMessage.prefix");

But I'm still getting an error in the console after turning it on.

Code:

Caused by: java.lang.NullPointerException
    at me.Mauzuk.JoinMessage.Main.<init>(Main.java:15) ~[?:?]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:1.8.0_261]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[?:1.8.0_261]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~[?:1.8.0_261]
    at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[?:1.8.0_261]
    at java.lang.Class.newInstance(Unknown Source) ~[?:1.8.0_261]
    at org.bukkit.plugin.java.PluginClassLoader.<init>(PluginClassLoader.java:76) ~[spigot-1.16.1.jar:git-Spigot-0287a20-7560f5f]
    at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:135) ~[spigot-1.16.1.jar:git-Spigot-0287a20-7560f5f]
    ... 24 more

 

can i see your full code and the config file?