Better

src/main/java/us/ajg0702/queue/spigot/Commands.java

@@ -16,9 +16,12 @@ public class Commands implements CommandExecutor {
 
 	@Override
 	public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
-		Player player = (Player) sender;
+		Player player;
+		if(sender instanceof Player) {
+			player = (Player) sender;
+		}
 		if(command.getName().equals("leavequeue")) {
-			if(!(sender instanceof Player)) return true;
+			if(player == null) return true;
 			StringBuilder arg = new StringBuilder();
 			for(String a : args) {
 				arg.append(" ");