Summary

When a null value is given to Results.Json, it no longer outputs "null" in the response body, instead the response body is empty

Repro steps

1. Run the ResultJsonRepro project as is
2. Observe that the browser will show

null

3. Edit ResultJsonRepro.csproj by replacing the TargetFramework "net6.0" with "net8.0" (or "net7.0")
4. Run the ResultJsonRepro project again
5. Observe no content in the browser

NOTE: for completeness I've also added an endpoint for "Mvc" ("/mvc") and "WebApi" ("/api") using the Json method on the Controller base class. Both of these remained to produce the expected output.

Use case

Migrating from LTS .NET 6 to LTS .NET 8 broke several api contracts due to the lack of a response body, which when put live as if will break clients not in our control (it will fail to deserialize JSON)