Github user justinleet commented on the issue:
https://github.com/apache/metron/pull/970
@merrimanr I fixed the metaalert template; I'd forgotten to update the
original placeholder one in addition to the test one. I haven't had a chance
to run it up and see if it fixes what you saw, but it explains the
_childDocuments_ problem. The message itself is a bit of a red herring: it's a
special field, so the lack of definition at all caused problem.---
