Unrecoverable error in input { elasticsearch {} } when using "fields" in query

Elastic Stack Logstash
1

This is my rather trivial logstash config:

input {
    elasticsearch {
        hosts => "localhost"
        query => '{"query": {"match": {"tags": "pipeline-v0.6"}}}'
        # query => '{"query": {"match": {"tags": "pipeline-v0.6"}}, "fields": ["message"]}'
        size => 10
    }
}

output {
    stdout {
        codec => rubydebug
    }
}

When used as-is, it works fine. When using the commented query instead, this error occurs (over and over again):

A plugin had an unrecoverable error. Will restart this plugin.
  Plugin: <LogStash::Inputs::Elasticsearch hosts=>["localhost"], query=>"{\"query\": {\"match\": {\"tags\": \"pipeline-v0.6\"}}, \"fields\": [\"message\"]}", size=>10, codec=><LogStash::Codecs::JSON charset=>"UTF-8">, index=>"logstash-*", scan=>true, scroll=>"1m", docinfo=>false, docinfo_target=>"@metadata", docinfo_fields=>["_index", "_type", "_id"], ssl=>false>
  Error: undefined method `[]' for nil:NilClass {:level=>:error}

When running the query in curl, it works just fine either way.
Context (just in case you've got a completely different approach): When refining my filter{} (which I store in another file, and didn't use to test this), I don't want to juggle the original test files, but instead just use this input and another elasticsearch {} output to work through all the indexed documents.

2

This is a little late, I don't know if you managed to solve it or not, just in case somebody else will face the same problem. I faced the same issue, solved it by using _source instead.

input {
    elasticsearch {
        hosts => "localhost"
        query => '{"query": {"match": {"tags": "pipeline-v0.6"}}, "_source": ["message"]}'
        size => 10
    }
}

The "fields" parameter is only for the stored fields, which fields is stored is specified by the mapping in the elasticsearch. So if you want to use the "fields" parameter, try updating the mapping in of the index.

More on _source