Maybe also on ES6 and ES7, we'd have to check.
{ "took": 6, "errors": true, "items": [ { "index": { "_index": "indexname", "_type": "doc", "_id": "document1", "status": 400, "error": { "type": "mapper_parsing_exception", "reason": "failed to parse [flattenedObject.byType_MonthDay]", "caused_by": { "type": "illegal_field_value_exception", "reason": "Cannot parse \"--02-29\": Value 29 for dayOfMonth must be in the range [1,28]" } } } },