@Override
	// TODO: This will likely be fixed in core Spring
	public void setContentTypeResolver(ContentTypeResolver resolver) {
		if (getContentTypeResolver() == null) {
			super.setContentTypeResolver(resolver);
		}
	}
Subclasses implement this to specify supported payload types

@return an array of supported classes or null if any target type is supported
spring-xd-dirt/src/main/java/org/springframework/xd/dirt/integration/bus/converter/AbstractFromMessageConverter.java