Introduce WebClient.ResponseSpec.awaitBodilessEntity()

This commit also allows awaitBody<Unit>() to be used.

Closes gh-26504

spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/client/WebClientExtensions.kt

@@ -138,7 +138,16 @@ inline fun <reified T : Any> WebClient.ResponseSpec.bodyToFlow(): Flow<T> =
  * @since 5.2
  */
 suspend inline fun <reified T : Any> WebClient.ResponseSpec.awaitBody() : T =
-		bodyToMono<T>().awaitSingle()
+	when (T::class) {
+		Unit::class -> awaitBodilessEntity().let { Unit as T }
+		else -> bodyToMono<T>().awaitSingle()
+	}
+
+/**
+ * Coroutines variant of [WebClient.ResponseSpec.toBodilessEntity].
+ */
+suspend fun WebClient.ResponseSpec.awaitBodilessEntity() =
+	toBodilessEntity().awaitSingle()
 
 /**
  * Extension for [WebClient.ResponseSpec.toEntity] providing a `toEntity<Foo>()` variant

spring-webflux/src/test/kotlin/org/springframework/web/reactive/function/client/WebClientExtensionsTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.Test
 import org.reactivestreams.Publisher
 import org.springframework.core.ParameterizedTypeReference
+import org.springframework.http.ResponseEntity
 import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
 import java.util.concurrent.CompletableFuture
@@ -125,6 +126,26 @@ class WebClientExtensionsTests {
 		}
 	}
 
+	@Test
+	fun `awaitBody of type Unit`() {
+		val spec = mockk<WebClient.ResponseSpec>()
+		val entity = mockk<ResponseEntity<Void>>()
+		every { spec.toBodilessEntity() } returns Mono.just(entity)
+		runBlocking {
+			assertThat(spec.awaitBody<Unit>()).isEqualTo(Unit)
+		}
+	}
+
+	@Test
+	fun awaitBodilessEntity() {
+		val spec = mockk<WebClient.ResponseSpec>()
+		val entity = mockk<ResponseEntity<Void>>()
+		every { spec.toBodilessEntity() } returns Mono.just(entity)
+		runBlocking {
+			assertThat(spec.awaitBodilessEntity()).isEqualTo(entity)
+		}
+	}
+
 	@Test
 	fun `ResponseSpec#toEntity with reified type parameters`() {
 		responseSpec.toEntity<List<Foo>>()