Firebase notification data is empty when switching between background and foreground.

Hi everyone,
I regularly push a Cloud Messaging notification containing data. When the app is in the background, sometimes the data is empty.
I read on Firebase that this has something to do with getting the data from "Intent", but there's no other information.
Could anyone help out on this subject? What is this Intent and what/how do I do to get the info from there?
Thanks,