[Bug]: CancellationToken? cancellationToken causes exception

[Szpi]

Describe the bug 🐞

After migration from version 8.0.0 to 9.0.2 CancellationToken? cancellationToken causes exception:
Index was outside the bounds of the array.

Stack Trace:

   at Internal.Runtime.CompilerHelpers.ThrowHelpers.ThrowIndexOutOfRangeException()
   at Refit.RequestBuilderImplementation.<>c__DisplayClass22_0.<BuildRequestFactoryForMethod>b__0(Object[] paramList)
   at Refit.RequestBuilderImplementation.<>c__DisplayClass18_0`2.<<BuildCancellableTaskFuncForMethod>b__0>d.MoveNext()

Client definition (obfuscated)

[Post("/api/a/{id}/b/c")]
Task<Dto> Create(Guid id, [Body] Dto2 requestBody, CancellationToken? cancellationToken);

Step to reproduce

1. Use Refit with version 9.0.2
2. Use client definition in description
3. Exception is thrown in runtime

Reproduction repository

https://github.com/reactiveui/refit

Expected behavior

This should work and not throw exception.

Refit Version

9.0.2

Additional information ℹ️

In old version 8.0.0 it worked.
Changing it to CancellationToken cancellationToken = default seems to work.