[Bug]: String in json format as input for [FromForm] is not recognized in UI

[KillerBoogie]

Describe the bug

For an endpoint that accepts a file, the title, and a description in multiple languages I use this method

public async Task<ActionResult<GuidIdResponse>> UploadImage([FromForm] string title, [FromForm] string? description, IFormFile file)

The title is entered in JSON format like:

{de":"Bildschirmfoto","en":"screen shot"}

When I enter the above string in the title field of the generated Swashbuckle UI I'm getting error 400:

{
  "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "errors": {
    "title": [
      "The title field is required."
    ]
  },
  "traceId": "00-259db306db8ce9b0015192084dfc72f2-cd711e4da768cce5-00"
}

The code of my endpoint method is not hit. The error is produced by the framework. When I send the same request with Postman it works fine!

This only happens if the JSON string is well formed and not escaped.

This is sent correctly: {\"de\":\"Bildschirmfoto\",\"en\":\"screen shot\"}

Those also pass through:

"de":"Bildschirmfoto","en":"screen shot"}
{"de":"Bildschirmfoto",x"en":"screen shot"}
{"de":"Bildschirmfoto",,"en":"screen shot"}

As soon as the JSON is correctly formed, but not escaped the string is not passed and treated as not entered.

Since it works fine with Postman t must be a bug in Swashbuckle.,

Expected behavior

Pass the entered string into the variable.

Actual behavior

A string in valid JSON format is treated as not provided:

{ "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1", "title": "One or more validation errors occurred.", "status": 400, "errors": { "title": [ "The title field is required." ] }, "traceId": "00-259db306db8ce9b0015192084dfc72f2-cd711e4da768cce5-00" }

Steps to reproduce

No response

Exception(s) (if any)

No response

Swashbuckle.AspNetCore version

6.7.0

.NET Version

8.0.303

Anything else?