GH-3054: Resolve deprecation for WebFlux module

Fixes #3054

Author: artembilan

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/outbound/WebFluxRequestExecutingMessageHandler.java

@@ -312,9 +312,8 @@ else if (requestBody instanceof MultiValueMap<?, ?>) {
 			inserter = buildBodyInserterForMultiValueMap((MultiValueMap<?, ?>) requestBody,
 					httpRequest.getHeaders().getContentType());
 		}
-
-		if (inserter == null) {
-			inserter = BodyInserters.fromObject(requestBody);
+		else {
+			inserter = BodyInserters.fromValue(requestBody);
 		}
 		return inserter;
 	}