Paper 1.18.1
GUIShop 1.5.9

error:
[17:21:23] [Thread-15/WARN]: Exception in thread "Thread-15" java.lang.NullPointerException: Cannot invoke "org.bukkit.configuration.file.FileConfiguration.getConfigurationSection(String)" because "this.config" is null
[17:21:23] [Thread-15/WARN]: at GUIShop-9.1.5.jar//com.pablo67340.guishop.config.ButtonConfig.createBackButton(ButtonConfig.java:56)
[17:21:23] [Thread-15/WARN]: at GUIShop-9.1.5.jar//com.pablo67340.guishop.config.ButtonConfig.createButtons(ButtonConfig.java:26)
[17:21:23] [Thread-15/WARN]: at GUIShop-9.1.5.jar//com.pablo67340.guishop.GUIShop.loadDefaults(GUIShop.java:407)
[17:21:23] [Thread-15/WARN]: at GUIShop-9.1.5.jar//com.pablo67340.guishop.GUIShop.handleConfig(GUIShop.java:465)
[17:21:23] [Thread-15/WARN]: at java.base/java.lang.Thread.run(Thread.java:833)