This is your problem. You do this: Code (Text): String value = args[0]; but then you check if the length of the array is zero. You need to be checking if args.length is 1, not 0. You should also be checking for the array length before assigning a value from it, because you may end up with an ArrayIndexOutOfBoundsException.
PHP: if(cmd.getName().equalsIgnoreCase("link")&& args.length > 0) { //check your configuration. }else { //Inform player of incorrect arguments. }