MediaType.text.plain broken reference in swagger

[swoogles]

Describe the bug
SwaggerUI shows errors when looking at endpoints with MediaType.text.plain

This might be another manifestation of #3260
But I do see just a plain string result in the input box, and I see text/plain in the mediatype.
So that particular behavior is different for me. It seems like that other issue might already be resolved?

To Reproduce
Steps to reproduce the behaviour:

1. Run the application here: https://github.com/swoogles/MediaTypeTextPlainReproducer
2. Go to: http://localhost:8080/docs
3. Click on either route to see the errors pop up, and the examples fail to load

Expected behaviour
No errors, and we should see the examples.

Screenshots

Desktop (please complete the following information):

• OS: Macos
• Browser Zen/firefox