SPR-8572 Support Void.class as response type in RestTemplate.

org.springframework.web/src/main/java/org/springframework/web/client/RestTemplate.java

@@ -607,7 +607,7 @@ public class RestTemplate extends InterceptingHttpAccessor implements RestOperat
 		private final HttpMessageConverterExtractor<T> delegate;
 
 		public ResponseEntityResponseExtractor(Class<T> responseType) {
-			if (responseType != null) {
+			if (responseType != null && !Void.class.equals(responseType)) {
 				this.delegate = new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
 			} else {
 				this.delegate = null;

org.springframework.web/src/test/java/org/springframework/web/client/RestTemplateIntegrationTests.java

@@ -251,7 +251,7 @@ public class RestTemplateIntegrationTests {
 		requestHeaders.set("MyHeader", "MyValue");
 		requestHeaders.setContentType(MediaType.TEXT_PLAIN);
 		HttpEntity<String> requestEntity = new HttpEntity<String>(helloWorld, requestHeaders);
-		HttpEntity<?> result = template.exchange(baseUrl + "/{method}", HttpMethod.POST, requestEntity, null, "post");
+		HttpEntity<Void> result = template.exchange(baseUrl + "/{method}", HttpMethod.POST, requestEntity, Void.class, "post");
 		assertEquals("Invalid location", new URI(baseUrl + "/post/1"), result.getHeaders().getLocation());
 		assertFalse(result.hasBody());
 	}