How to convert a json field to string by using ruby filter?

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4

I've been solved my issue.

    ruby {
        code => "
            field_to_be_converted = ['[logdetail][params][result]',
                                     '[logdetail][params][body]',
                                     '[logdetail][params][item]',
                                     '[logdetail][params][items]']
            for field in field_to_be_converted
                if event.include?(field) && event[field].class != String
                    event[field] = event[field].to_s
                end
            end
        "
    }

I'm not sure why this code could work.