Good, Mauro
So, I'm reviewing it.
Several general comments:
* Add your name to author list
* Update Copyright of affected classes to actual date

To make the current change more convenient we have an util method:
````java
IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "flatten-map", "shouldFlattenKeys");
````
It's not so important for now, but would be better for future contributions: save your and our time.