Blocking call which returns a (possibly empty) batch of events

Return value
	type	description
	Set[Record[event]]	the batch of events
Parameters
name	type	description
session_id	session	valid session reference
Errors
name	arguments	description
SESSION_NOT_REGISTERED	handle	This session is not registered to receive events. You must call event.register before event.next. The session handle you are using is echoed.
EVENTS_LOST		Some events have been lost from the queue and cannot be retrieved.

• Message has only a synchronous version
• This is a custom message