How to not store the completion suggester in the index in Elasticsearch

I want to have a field tags as completion, and I do not want this field to participate in the scoring, so I am trying to apply the mapping

"tags": {
    "type": "completion",
    "index": false
}

And I am getting an error

ElasticsearchStatusException[Elasticsearch exception [type=mapper_parsing_exception, reason=Mapping definition for [tags] has unsupported parameters:  [index : false]]]

How should be the mapping?

the completion field does not support the index setting. If you execute a full text search query, any field of type completion will not participate in scoring. What makes you think otherwise?