Github user cestella commented on the issue:
https://github.com/apache/metron/pull/675
In my opinion, I don't think we want this behavior. I think it may be too
severe given how dirty and sparse our data tends to be.
Does this mean that if you have a stellar expression `FOO(bar)` and the
field `bar` doesn't exist, will we get an exception? If so, given that
messages come through with certain fields which are optional (i.e. some
messages have field `foo` and others might not have a field `foo` depending on
the parser), I think this will result in a fair number of errors.
I'd rather leave it up to the Stellar function creator to figure out if the
field is able to be optional or not rather than having a blanket policy of
throwing an exception. Consider the function `TO_UPPER`. I'd rather
`TO_UPPER` tolerate missing fields by passing them through (i.e.
`TO_UPPER(null) == null`) rather than throw an exception.
One approach to this would be changing the `StellarFunction` interface to a
`List<Optional<Object>>` instead of a `List<Object>` and have the variability
made explicit.
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