Form validation fails for slash commands without text/params

[modasserbillah]

Slash commands fail when there is no text or params added to the command. For example, /test would fail because text is set as required in the CommandForm definition.

If this is not intended behavior, I can open a PR to make it optional.

Thanks for the neat library, great work 👏

[ddemid]

Please feel free to open a PR.

Thank you!