How to show "N/A" in a field has null value

[v.le]

Hi, I am new for Elasticsearch!
I had imported my data content to Elasticsearch but I cant work out how to show the N/A value of the sales field. Here's the data :

country   group         brand   PT   date  sales
Japan	Toyota Group	Toyota	EV	202110	129
Japan	Toyota Group	Toyota	EV	202111	N/A
Japan	Toyota Group	Toyota	EV	202112	-

I set the "sales" field type to "number". And the "N/A" value is automatically turn to "0". How can I show the "N/A" but still keeping the field type-"number".

Thank you so much and sorry for my broken English !!!

[v.le]

I tried this in the dev tool

POST sales_finale/_update_by_query
{
  "query": {
    "bool": {
      "must_not": {
        "exists": {
          "field": "sales"
        }
      }
    }
  },
  "script": {
    "source": "ctx._source.put('sales', 'N/A');"
  }
}

but the error is

"failures" : [
    {
      "index" : "sales_finale",
      "type" : "_doc",
      "id" : "rM3GAX4BuGsV_tj3wH97",
      "cause" : {
        "type" : "mapper_parsing_exception",
        "reason" : "failed to parse field [sales] of type [long] in document with id 'rM3GAX4BuGsV_tj3wH97'. Preview of field's value: 'N/A'",
        "caused_by" : {
          "type" : "illegal_argument_exception",
          "reason" : "For input string: \"N/A\""
        }
      },
      "status" : 400
    },