If I use 'combined type' to the request, the requestBody isn't generated.

[antasis9]

Describe the bug
If I use 'combined type' as the request body, the requestBody isn't generated.

To Reproduce
I used below source code to reproduce this bug.

type BookRequest =
  | {
      type: "poem";
    }
  | {
      key: "novel";
    };

export type BookApiSpec = Tspec.DefineApiSpec<{
...
  paths: {
    "/books": {
      post: {
...
        body: BookRequest;
...
      };
    };
  };
}>;

Steps to reproduce the behavior:
npx tspec generate

Expected behavior
I've been expected 'requestBody' to generated json file.
However, I can't find them at there, please refer to Screenshots section.
When I used 'single type', it's working perfectly.

Screenshots
There is no 'requestBody' section.

Desktop (please complete the following information):

• OS: Windows
• Browser edge
• Version N/A

Additional context
Add any other context about the problem here.