Supporting form_with in Rails 8.0

[jiko797torayo]

@amatsuda

I have created a PR to fix this issue💪
Please review it when you have a moment.

Close #32

Thank you for the wonderful gem✨

When I tried to upgrade a Rails application that using this gem to Rails 8.0, the following error occurred.

ActionView::Template::Error (Passed nil to the :model argument, expect an object or false)
Caused by: ArgumentError (Passed nil to the :model argument, expect an object or false)

Information for: ActionView::Template::Error (Passed nil to the :model argument, expect an object or false):
    1: <%= form_with url: '/search', id: 'form_with' do |f| %>
    2: <%= f.search_field :query, id: 'query' %>
    3: <% end %>

The cause is that the default value of the model: argument of form_with was changed from nil to false in Rails 7.2, and passing nil to the model: argument causes an error in Rails 8.0.

• Handle nil form_with model argument rails/rails#49943
• deprecate passing nil as model arg instead of raising ArgumentError rails/rails#50931
• Remove all deprecations rails/rails#53374
  • rails/rails@0c150ba