@da_Do First of all, its FAR more simple to just check if sender is Player. Your problem is mainly because you didn't close the checking. Close it and your problem is gonna be solved. Also there is no need to register command in class main class. And you don't need to do the System.out.println(). Bukkit already does it for you.
@XxTimexX This isn't even a problem with bukkit. He forgot to check his encapsulation. He is currently checking if the sender is a console, returning, not ending the encapsulation and then casting the sender to a player. Although you should learn how to work with bukkit, What is more important is that you learn Java. Please select a tutorial from the following link, learn Java (which should only take a week), and then come back to bukkit. https://bukkit.org/threads/plugin-dev-sticky-learning-java-where-to-learn.395662/
