ElasticSearch partial field update: remove element from array, does not work

partial_update_maybe_issue

curl -XPUT 'http://localhost:9200/testindex' -d '{
"settings":
{
"number_of_shards": 1,
"number_of_replicas": 0
}
}
'

curl -XPUT 'http://localhost:9200/testindex/posting/_mapping' -d '
{ "posting": {
"properties":
{
"id": {"type": "long", "store": "yes"},
"labels": {"type": "integer", "index_name": "label", "store": "yes"}
}
}
}
'

curl -XPOST 'http://localhost:9200/_bulk?pretty=true' -d '
{"index" : { "_index" : "testindex", "_type" : "posting", "_id" : "1" }}
{"labels":[], "id":1}
'



curl -XPOST 'http://localhost:9200/testindex/posting/1/_update' -d '{
    "script" : "ctx._source.labels += label",
    "params" : {
        "label" : 5
    }
}'

curl -XGET 'http://localhost:9200/testindex/posting/1'


curl -XPOST 'http://localhost:9200/testindex/posting/1/_update' -d '{
    "script" : "ctx._source.labels -= label",
    "params" : {
        "label" : 5
    }
}'

#result is {"error":"ElasticSearchIllegalArgumentException[failed to execute script]; nested: StringIndexOutOfBoundsException[String index out of range: -1]; ","status":400}