JSON filter gives warning that it requires a target

Elastic Stack Logstash
1

[2018-01-06T03:41:04,492][WARN ][logstash.filters.json ] Parsed JSON object/hash requires a target configuration option {:source=>"extras", :raw=>""}

I don't have a target set because I read in the documentation that the default behavior is to put the parsed fields at the top level of the doc. Why is it warning me about this then? The warning barely ever shows up, even though it has successfully parsed that field in millions of other docs.

2

It looks like the string you're attempting to parse is empty (note :raw=>"").

3

Why does the error say it needs a target then? Shouldn't the error say "trying to parse empty string" or something?

4

Parsing an empty string apparently results in a valid value (in the sense that the parsing doesn't fail), but since it's not a hash you get the generic error message in question.