Looks like there is no reason add `globalMethodMetadata`, if there no any `default-header` and `default-payload-expression`.
Something like this:
````java
BeanDefinitionBuilder methodMetadataBuilder = null;
		List<Element> invocationHeaders = DomUtils.getChildElementsByTagName(element, "default-header");
		if (!CollectionUtils.isEmpty(invocationHeaders) ||
				StringUtils.hasText(element.getAttribute("default-payload-expression"))) {
			methodMetadataBuilder = BeanDefinitionBuilder.genericBeanDefinition(
					"org.springframework.integration.gateway.GatewayMethodMetadata");
			this.setMethodInvocationHeaders(methodMetadataBuilder, invocationHeaders);
			IntegrationNamespaceUtils.setValueIfAttributeDefined(methodMetadataBuilder, element,
					"default-payload-expression", "payloadExpression");
			builder.addPropertyValue("globalMethodMetadata", methodMetadataBuilder.getBeanDefinition());
		}
````