Default command should display help

[rupurt]

I'm trying to write a CLI with subcommands and I'd like to have the default command with no args display the help message. What is the best way to achieve that?

Currently I get the following parse error

Failed to parse command ""

defmodule Bos.CLI do
  use Nexus

  defcommand(:broker, type: :null, doc: "broker subcommands.") do
    defcommand(:start, default: "", doc: "start a broker in the foreground.")
    defcommand(:stop, default: "", doc: "stop a running broker.")
  end

  @impl Nexus.CLI
  def version, do: "0.0.1"

  @impl Nexus.CLI
  def banner, do: "universal cli for bos"

  @impl Nexus.CLI
  def handle_input(:broker, %{value: value, subcommand: :start}) do
    IO.puts("TODO 'broker start'")
    IO.inspect(value, label: :value)
    :ok
  end

  def handle_input(:broker, %{value: value, subcommand: :stop}) do
    IO.puts("TODO 'broker stop'")
    IO.inspect(value, label: :value)
    System.halt(0)
    :ok
  end

  def handle_input(:broker, args) do
    IO.puts("TODO 'broker catch all'")
    IO.inspect(args, label: :args)
    System.halt(0)
    :ok
  end

  @impl Nexus.CLI
  def handle_input(:help) do
    IO.puts(Nexus.help(__MODULE__))
    System.halt(0)
    :ok
  end

  def handle_input(catch_all) do
    IO.puts("CATCH all/1: #{inspect(catch_all)}")
    System.halt(0)
    :ok
  end

  Nexus.help()
  Nexus.parse()
end