Fix exception if no RequestDataValueProcessor is present

This modification fixes the way AbstractView retrieves the
RequestDataValueProcessor bean, correctly returning null if there
is no bean of such type at the Application Context.

This avoids an exception in RedirectView (which extends AbstractView)
when trying to post-process the URL generated for redirection, when
no RequestDataValueProcessor exists.

Issue: SPR-15136

Author: danielfernandez

spring-web-reactive/src/main/java/org/springframework/web/reactive/result/view/AbstractView.java

@@ -191,11 +191,12 @@ protected RequestContext createRequestContext(ServerWebExchange exchange, Map<St
 	 * <p>The default implementation looks in the {@link #getApplicationContext()
 	 * Spring configuration} for a {@code RequestDataValueProcessor} bean with
 	 * the name {@link #REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME}.
+	 * @return the RequestDataValueProcessor, or null if there is none at the application context.
 	 */
 	protected RequestDataValueProcessor getRequestDataValueProcessor() {
-		if (getApplicationContext() != null) {
-			String beanName = REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME;
-			return getApplicationContext().getBean(beanName, RequestDataValueProcessor.class);
+		ApplicationContext context = getApplicationContext();
+		if (context != null && context.containsBean(REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME)) {
+			return context.getBean(REQUEST_DATA_VALUE_PROCESSOR_BEAN_NAME, RequestDataValueProcessor.class);
 		}
 		return null;
 	}