You usually should send an object that will represent the event that you are signalling. I usually send something more representative like an object that represent the event and in the case that you need to send a map of parameter you should create an object to wrap that map and add more semantic meaning to the event. You can take a look at the emergency services application to see how we are sending events and how we are using that information in different activities of the process.
As Mauricio mentioned, the best and more clear way to handle events is to have your own Event class with all the attributes you need. Using a Map is a dirty solution in my opinion.