As a follow-up to [rails/rails#40479][], ensure that empty Hash and
Array arguments are treated as `nil`.

For example, when conditionally rendering an [aria-describedby][]
attribute to associate an input with a related validation error, treat
an empty Array as `nil`, an omit the attribute entirely:

```html+erb
<% post = Post.new %>

<%= form_with model: post do |form| %>
  <%= form.text_field :title, aria: { describedby: { post_title_error: post.errors[:title].any? } } %>
  <%= tag.span(post.errors[:title].to_sentence, id: :post_title_error) if post.errors[:title].any? %>
<% end %>
```

In this example, when there are no errors, the desired outcome is for
the `<input type="text" name="post[title]">` element to _omit_ the
`[aria-describedby="post_title_error"]` attribute, and to only include
it when there are errors on the `title` attribute.

Without this change, the desired outcome can be achieved with a
combination of a `#token_list` and `#presence` call:

```diff
<% post = Post.new %>

<%= form_with model: post do |form| %>
-  <%= form.text_field :title, aria: { describedby: {post_title_error: post.errors[:title].any?} }
+  <%= form.text_field :title, aria: { describedby: token_list(post_title_error: post.errors[:title].any?).presence } %>
  <%= tag.span(post.errors[:title].to_sentence, id: :post_title_error) if post.errors[:title].any? %>
<% end %>
```

[rails/rails#40479]: https://github.com/rails/rails/pull/40479
[aria-describedby]: https://www.w3.org/WAI/WCAG21/Techniques/aria/ARIA21#example-2-identifying-errors-in-data-format