Fix exchangeToMono sample in reference

Closes gh-26189

src/docs/asciidoc/web/webflux-webclient.adoc

@@ -554,28 +554,30 @@ depending on the response status:
 					return response.bodyToMono(Person.class);
 				}
 				else if (response.statusCode().is4xxClientError()) {
+					// Suppress error status code
 					return response.bodyToMono(ErrorContainer.class);
 				}
 				else {
-				   return Mono.error(response.createException());
+					// Turn to error
+					return response.createException().flatMap(Mono::error);
 				}
 			});
 ----
 [source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
 .Kotlin
 ----
-    val entity = client.get()
+val entity = client.get()
   .uri("/persons/1")
   .accept(MediaType.APPLICATION_JSON)
   .awaitExchange {
 		if (response.statusCode() == HttpStatus.OK) {
-                return response.awaitBody<Person>();
+			 return response.awaitBody<Person>()
 		}
 		else if (response.statusCode().is4xxClientError) {
-                return response.awaitBody<ErrorContainer>();
+			 return response.awaitBody<ErrorContainer>()
 		}
 		else {
-                return response.createExceptionAndAwait();
+			 throw response.createExceptionAndAwait()
 		}
   }
 ----