Do not override with 404 when returning response inside CompletableFuture

http-server-tck/src/main/java/io/micronaut/http/server/tck/tests/BodyTest.java

@@ -20,21 +20,25 @@
 import io.micronaut.core.async.annotation.SingleResult;
 import io.micronaut.http.HttpHeaders;
 import io.micronaut.http.HttpRequest;
+import io.micronaut.http.HttpResponse;
 import io.micronaut.http.HttpStatus;
 import io.micronaut.http.MediaType;
 import io.micronaut.http.annotation.Body;
 import io.micronaut.http.annotation.Consumes;
 import io.micronaut.http.annotation.Controller;
+import io.micronaut.http.annotation.Get;
 import io.micronaut.http.annotation.Post;
 import io.micronaut.http.annotation.Status;
 import io.micronaut.http.tck.AssertionUtils;
 import io.micronaut.http.tck.BodyAssertion;
 import io.micronaut.http.tck.HttpResponseAssertion;
 import org.junit.jupiter.api.Test;
 import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
 
 import java.io.IOException;
 import java.util.Objects;
+import java.util.concurrent.CompletableFuture;
 
 import static io.micronaut.http.tck.TestScenario.asserts;
 
@@ -142,6 +146,28 @@ void testRequestBodyFormDataNoBodyAnnotation() throws IOException {
                     .build()));
     }
 
+    @Test
+    void testEmptyFuture() throws IOException {
+        asserts(SPEC_NAME,
+            HttpRequest.GET("/response-body/empty-future")
+                .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_FORM_URLENCODED),
+            (server, request) -> AssertionUtils.assertDoesNotThrow(server, request,
+                HttpResponseAssertion.builder()
+                    .status(HttpStatus.OK)
+                    .build()));
+    }
+
+    @Test
+    void testEmptySingleResultPublisher() throws IOException {
+        asserts(SPEC_NAME,
+            HttpRequest.GET("/response-body/empty-single-result")
+                .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_FORM_URLENCODED),
+            (server, request) -> AssertionUtils.assertDoesNotThrow(server, request,
+                HttpResponseAssertion.builder()
+                    .status(HttpStatus.OK)
+                    .build()));
+    }
+
     @Controller("/response-body")
     @Requires(property = "spec.name", value = SPEC_NAME)
     static class BodyController {
@@ -195,6 +221,17 @@ Publisher<Point> postMany(@Body Publisher<Point> data) {
         String postBytes(@Body byte[] bytes) {
             return new String(bytes);
         }
+
+        @Get(uri = "/empty-future")
+        CompletableFuture<HttpResponse<?>> emptyFuture() {
+            return CompletableFuture.completedFuture(HttpResponse.ok());
+        }
+
+        @Get(uri = "/empty-single-result")
+        @SingleResult
+        Publisher<HttpResponse<?>> emptySingleResult() {
+            return Mono.just(HttpResponse.ok());
+        }
     }
 
     @Introspected

http-server/src/main/java/io/micronaut/http/server/RouteExecutor.java

@@ -692,6 +692,7 @@ private CompletionStage<MutableHttpResponse<?>> fromCompletionStage(@NonNull Htt
                     return CompletableFuture.completedStage(newNotFoundError(request));
                 }
             }
+            boolean explicitResponse = false;
             if (asyncBody instanceof HttpResponse<?> httpResponse) {
                 mutableResponse = httpResponse.toMutableResponse();
                 final Argument<?> bodyArgument = routeInfo.getReturnType() // CompletionStage
@@ -706,14 +707,15 @@ private CompletionStage<MutableHttpResponse<?>> fromCompletionStage(@NonNull Htt
                         return mutableResponse.body(innerBody);
                     });
                 }
+                explicitResponse = true;
             } else if (asyncBody instanceof HttpStatus status) {
                 mutableResponse = forStatus(routeInfo, status);
             } else {
                 mutableResponse = forStatus(routeInfo, null)
                     .body(asyncBody);
             }
             if (mutableResponse.body() == null) {
-                if (routeInfo.isVoid()) {
+                if (routeInfo.isVoid() || explicitResponse) {
                     return CompletableFuture.completedStage(voidResponse(routeInfo));
                 }
                 return CompletableFuture.completedStage(newNotFoundError(request));