title: Python Click: Error: Missing argument while calling the --help flag
body: <p>This is my code:</p>
  
  <pre><code>@click.group()
  @click.pass_context
  @click.argument('CHALLENGE', type=int)
  def challenge(ctx, challenge):
      ctx.obj = Challenge(challenge=challenge)
  
  @click.group(invoke_without_command=True, cls=PhaseGroup)
  @click.pass_obj
  @click.argument('PHASE', type=int)
  def phase(ctx, phase):
      # Something
  
  challenge.add_command(phase)
  </code></pre>
  
  <p>Together these commands are supposed to work like.</p>
  
  <pre><code>cli challenge 1 phase 1
  </code></pre>
  
  <p>Which works as intended by executing properly.</p>
  
  <p>But when I use --help or define any other flags on phase, it throws</p>
  
  <pre><code>cli challenge 1 phase 1 --help
  
  It throws Error: Missing argument "PHASE".
  </code></pre>
  
  <p>I searched SOF and found <a href="https://stackoverflow.com/questions/47272584/python-click-app-is-failing-with-indication-of-missing-argument-but-cannot-loc">python click app is failing with indication of &quot;missing argument&quot; but cannot locate the issue</a> This is a user who had the same issue, but I didn't quite understand the answer.</p>
  
  <p>I cannot make the arguments optional since it is a crucial part of making the CLI work.</p>