Each ArgumentType provided to a command can be made optional with either optional or optionalNullable functions.

command("DisplayText") {
    description = "Display some text."
    execute(AnyArg.optional("Hello")) {
        val text = args.first
        respond("Your text is: $text")

This command accepts an optional AnyArg, meaning the command can be called with 0 or 1 arguments. The provided default value will be used if no input is provided by the user. In this case, when called with no arguments, the value of the text is "Hello".