Currently trending at https://logstash.wikimedia.org/#/dashboard/elasticsearch/eventlogging-errors with over 1100 hits in the past 24 hours (which are silently dropped from further processing).
event revision 13457736
event schema Edit
message level ERROR
messageNone is not of type u'integer'
See also https://meta.wikimedia.org/wiki/Schema:Edit
Sample:
{"event":{"version":1,"action":"abort","editor":"visualeditor","platform":"desktop","integration":"page",..,"user.id":0,"user.editCount":0,"mediawiki.version":"1.27.0-wmf.3","user.class":"IP","action.abort.type":"nochange","action.abort.mechanism":"navigate-back","action.abort.timing":null},"revision":13457736,"schema":"Edit","webHost":"vi.wikipedia.org","wiki":"viwiki"}
Presumably the error is about property action.abort.timing being null.