How to find the data that causes the mapper_parsing_exception

[AlanSBN (Alan)]

I am using the Node Elasticsearch client from inside Node Express, and I constructed a query that generates the following error:

(node:85104) ResponseError: mapper_parsing_exception: [mapper_parsing_exception] Reason: object mapping for [data] tried to parse field [data] as object, but found a concrete value at onBody

The error occurs after the call to search returns the correct result.

The query is built as follows:

    const query = {
      _source: false,
      query: {
        bool: {
          filter: [
            { term: { owner: user }},
            { terms: { type: [ 'TEXT', 'MEDI' ]}}
          ]
        }
      },
      fields: [ 'serial', 'tags' ]
    }

The value user is a number. There is a field named data in the documents, mapped as an object . However all instances of this field are in fact an object.

Further, there is no error if I do the exact same query via the Kibana devtool. It returns the same set of documents that the javascript call does. This suggests to me either:

1. The error is in the node client.
2. The error is not visible from the Kibana client.

I am looking for some suggestion as to where this error is coming from and how to solve it. Any help appreciated.