bug in safari Unhandled Promise Rejection: ReadableStream is not supported

[AllesOderNicht]

Unhandled Promise Rejection: Error: Request failed with status NotSupportedError: ReadableStream uploading is not supported，

However, in my code, the content-type is set to JSON. I don't know why the response body becomes a ReadableStream, and this only happens after the code is built in Next.js 15.

[sholladay]

Show your code.