Loading JSON stream from Logstash to Elasticsearch

I'm trying to load JSON stream (lines of json objects file) through logstash to elasticsearch. Some of my json object field contains unicode as you can see below.

{"status_link": "https://www.facebook.com/asia/videos/1118055131588324/", "num_loves": "4", "num_sads": "0", "num_wows": "0", "num_angrys": "0", "num_Idea": "6", "num_reactions": "46", "num_hahas": "0", "link_name": "", "num_likes": "42", "timestamp": "2016-07-25 02:07:38", "num_shares": "8", "_id": "156915824368931_1118055131588324", "status_message": ""u0411u0440u0438u0433u0430u0434" u0440u0435u0430u043bu0438u0442u0438 u0448u043eu0443u043du044b u0448u0438u043du044d u0434u0443u0433u0430u0430u0440 07-u0440 u0441u0430u0440u044bu043d 28-u043du044b u043fu04afu0440u044du0432 u0433u0430u0440u0430u0433u0438u0439u043d u043eu0440u043eu0439 18:00 u0446u0430u0433u0430u0430u0441", "status_type": "video"}

When I start logstash, it gives me an error:

"status"=>400, "error"=>{"type"=>"mapper_parsing_exception", "reason"=>"failed to parse", "caused_by"=>{"type"=>"illegal_state_exception", "reason"=>"Mixing up field types: class org.elasticsearch.index.mapper.core.StringFieldMapper$StringFieldType != class org.elasticsearch.index.mapper.inteal.IdFieldMapper$IdFieldType on field _id"}}}}, :level=>:wa}

My logstash.conf:

input
{
    file
    {
        path => "test.json"
        start_position => "begiing"
        sincedb_path => "/dev/null"
        exclude => "*.gz"
        type => "posts"
        codec => "json"
    }
}

filter {
  json {
    source => "message"
  }
}

output {
  elasticsearch {
  hosts => ["localhost:9200"]
  index => "fb"
  codec => "json"
   }
}

I tried to load json object without unicode, it successfully parses and indexes in elasticsearch.