Http poller plugin automatically splits json response

I'm using the http_poller plugin with an endpoint that returns a json array and then I'm processing the response in a ruby script. It seems like http_poller is automatically splitting the body into separate events for each element in the response. I'm not using a split filter at all, and getting the error Could not process event: undefined method `has_key?' for ["id", 5]:Array. Is this expected/documented? Am I doing something wrong?

input {
    http_poller {
      urls => {
        poll_it => {
          method => get
          url => "http://endpoint/stuff"
        }
      }
      request_timeout => 60
      schedule => { every => "1m" }
      codec => "json"
      metadata_target => "poll_metadata"
      target => "body"
    }
}
filter {
  ruby {
    path => "/some/script.rb"
  }
}
output {
  pipeline {
    send_to => [someOtherPipeline]
  }
}

Script:

def filter(event)
  body = event.get("body")
  logger.error("test: ", {"value" => body})
  stuff = []
  for thing in body do
    if thing.has_key? "foo"
      stuff.push(thing["foo"])
    end
  end

  event.set("stuff", stuff.join(','))

  return [event]
end