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kotlinlang

I'm getting `ResponseAlreadySentException`s when using a redirect. Stack trace:
```io.ktor.server.engine.BaseApplicationResponse$ResponseAlreadySentException: Response has already been sent
at io.ktor.server.engine.BaseApplicationResponse.commitHeaders (BaseApplicationResponse.kt:44)
at io.ktor.server.engine.BaseApplicationResponse.respondOutgoingContent$suspendImpl (BaseApplicationResponse.kt:108)
at io.ktor.server.engine.BaseApplicationResponse.respondOutgoingContent (BaseApplicationResponse.kt)```
The code generating the response is:
```            call.respondRedirect(signedUrl)```
where `signedUrl` is a string with a URL. The redirect works - the client gets the correct result and redirects to the new path. Just wondering why there is an exception.

I've seen this before as well, in responses other than redirects. Never figured out why it happens.

Well, I figured it out. I was actually calling `respond()` on the `ApplicationCall` twice, the second time was with the return value of a function which was `Unit`. Seems that `respond(Unit)` actually sends something which was unexpected.