MarshallingWsOutboundGatewayNoTemplateSpec overwrites useful WebserviceTemplate defaults with null

[gviczai]

In what version(s) of Spring Integration are you seeing this issue?

5.5.6, 5.4.x, but other versions are affected as well

Describe the bug

In MarshallingWsOutboundGatewaySpec.MarshallingWsOutboundGatewayNoTemplateSpec class the assemble() method overwrites messageSenders and faultMessageResolver's otherwise useful and valid default not null values
with null values in the WebServiceTemplate created by the builder itself if no values provided in the builder explicitly:
https://github.com/spring-projects/spring-integration/blob/5.4.x/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/MarshallingWsOutboundGatewaySpec.java#L144
https://github.com/spring-projects/spring-integration/blob/5.4.x/spring-integration-ws/src/main/java/org/springframework/integration/ws/AbstractWebServiceOutboundGateway.java#L181

Also, one MUST provide an encodingMode in the builder, because BaseWsOutboundGatewaySpec does exactly the same (overwrites the correct default value without null checking) with the UriFactory's encodingMode:
https://github.com/spring-projects/spring-integration/blob/5.4.x/spring-integration-ws/src/main/java/org/springframework/integration/ws/dsl/BaseWsOutboundGatewaySpec.java#L162
https://github.com/spring-projects/spring-integration/blob/5.4.x/spring-integration-ws/src/main/java/org/springframework/integration/ws/AbstractWebServiceOutboundGateway.java#L140

To Reproduce

create a Ws.marshallingOutboundGateway()

Expected behavior

faultMessageResolver, messageSenders and enCodingmode:

• may be left unspecified in builder, in which case the defaults in WebServiceTemplate and UriFactory should be left intact
  (Note: A simple null check before the setter calls would be sufficient.)
• if one needs null values, they should provide WebServiceTemplate and UriFactory explicitly (with mentioned fields set to null)

Sample

IntegrationFlow myFlow = IntegrationFlows
        .from(MessageChannels.direct("myChannel"))
        .handle(
            Ws.marshallingOutboundGateway()
                .marshaller(jaxb2Marshaller())
                .destinationProvider(createDestinationProvider(myBackendUri))
                // IntegrationFlows's Ws.marshallingOutBoundGateway a little bit buggy, it
                // overwrites nice defaults already set, so we have to provide encodingMode,
                // faultMessageResolver and MessageSenders here, otherwise they will be nulled,
                // which results in an error...
                .encodingMode(DefaultUriBuilderFactory.EncodingMode.TEMPLATE_AND_VALUES)
                .messageSenders(getWebserviceTemplateDefaultMessageSenders())
                .faultMessageResolver(getWebserviceTemplateDefaultFaultMessageResolver()))
        .get();