Create an Action that can be streamed in order to modify a mutable result set.
If set to true, an extra event is sent after the end of the result
set, poviding you with a chance to insert additional rows after
seeing all results. Only
end (to check for this special event) and
insert may be called in the ResultSetMutator in this case.
mutate(sendEndMarker = false).
An Action that runs this query.