Make it clear that a push message does not require a payload

[collimarco]

The standard should explicitly state that you can send a push signal without the notification payload (and without the related headers used for the payload encryption).

This fact is only implicit in the current standard. However it is widely used in production by many services that were born before the payloads.

The section 11.2.2 Receiving a Push Message, point 5, says If the push message contains a payload. However I can't find the place where the option "no payload" is described.

I think that you should state that more clearly in order to avoid future bugs.