Github user ottobackwards commented on the issue:
https://github.com/apache/metron/pull/863
The parser topology PRODUCES the original_string. By that very action, and
it's requirement, it can only be used and required by downstream usages either
from rest ( post indexing ) or during enrichment. It seems inconsistent to
validate without including that, if what you want to do is validate the entire
set of required fields. If you only want to handle what is required at a given
step, but not what is required 'overall' then this is OK, but something doesn't
seem right here conceptually.
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