ElasticSearch updateByQuery fails when updating a text field that has zero as value in it

Question

My index has around 170 Million documents. An example document would be like :

{
        "_index" : "ppdata",
        "_type" : "_doc",
        "_id" : "E-cA_H8BvtbXwHDqN7ne",
        "_score" : 1.0,
        "_source" : {
          "gender" : 0,
          "age" : 0,
          "carrier" : "vodafone",
          "placecategory" : "Financial Institution",
          "brandsvisited" : "JPMC Bank",
          "behavior" : 0,
          "polygonid" : 1574
        }

The following are the mapping for the index:

{
  "ppdata" : {
    "mappings" : {
      "dynamic" : "false",
      "properties" : {
        "age" : {
          "type" : "integer"
        },
        "brandsvisited" : {
          "type" : "text",
          "analyzer" : "standard"
        },
        "carrier" : {
          "type" : "keyword"
        },
        "gender" : {
          "type" : "integer"
        },
        "behavior" : {
          "type" : "text",
          "analyzer" : "standard"
        },
        "placecategory" : {
          "type" : "text",
          "analyzer" : "standard"
        },
        "polygonid" : {
          "type" : "integer"
        }
      }
    }
  }
}

In this the field behavior is defined as text - however the data has 0 in it.

In this I am trying to update the behavior field with tag BFSI Consumer - if the document has a tag Bank in brandsvisited or Financial in placecategory. I have used the following curl script

curl -X POST "http://localhost:9200/ppdata/_update_by_query?conflicts=proceed&pretty" -H 'Content-Type: application/json' -d'
{
    "script": {
        "source": "ctx._source.behavior += \",BFSI Consumers\"",
        "lang": "painless"
    },
    "query": {
        "bool" : {
            "should" : [
                { "match" : {"brandsvisited" : "Bank"} },
                { "match" : {"placecategory" : "Financial"} }
            ]
        }
    }
}
'

This is working in a smaller version of the index where I do not have 0 value in behavior field. However it fails in my primary database. The following is the error:

{
  "error" : {
    "root_cause" : [
      {
        "type" : "script_exception",
        "reason" : "runtime error",
        "script_stack" : [
          "ctx._source.behavior += \",BFSI Consumers\"",
          "           ^---- HERE"
        ],
        "script" : "ctx._source.behavior += \",BFSI Consumers\"",
        "lang" : "painless",
        "position" : {
          "offset" : 11,
          "start" : 0,
          "end" : 44
        }
      }
    ],
    "type" : "script_exception",
    "reason" : "runtime error",
    "script_stack" : [
      "ctx._source.behavior += \",BFSI Consumers\"",
      "           ^---- HERE"
    ],
    "script" : "ctx._source.behavior += \",BFSI Consumers\"",
    "lang" : "painless",
    "position" : {
      "offset" : 11,
      "start" : 0,
      "end" : 44
    },
    "caused_by" : {
      "type" : "class_cast_exception",
      "reason" : "cannot implicitly cast def [int] to java.lang.String"
    }
  },
  "status" : 400
}