@matzew I think the main reason was  (in the beginning) to not have it in the message object https://github.com/aerogear/aerogear-unified-push-java-client/blob/master/src/main/java/org/jboss/aerogear/unifiedpush/SenderClient.java#L87 
Now that make me wonder if we want the same for category , deviceType and  variants ? Must be it be included in the "message" tag/object ?