Skip duplicated edges in ETL

How can I skip duplicated edges during ETL? According to the documentation:
"skipDuplicates" Defines whether to skip duplicate edges when the UNIQUE constraint is set on both the out and in properties.

I defined my json file like this:

{
  "config": {
    "log": "debug"},
  "source": { "file": { "path": "/home/file.csv" } },
  "extractor": { "csv": {} },
  "transformers": [
     { "merge": { "joinFieldName": "code", "lookup": "Code.code" } },        
         { "vertex": { "class": "Code" } },
         { "edge": {
             "class": "Has",
             "joinFieldName": "name",
             "lookup": "Country.name",
             "direction": "in",
             "skipDuplicates":true,
             "unresolvedLinkAction": "CREATE"} }
  ],
  "loader": {
    "orientdb": {
        "dbURL": "plocal:/home/path",
        "dbUser": "admin",
        "dbPassword": "admin",
        "dbAutoDropIfExists": false,
        "dbAutoCreate": true,
        "dbType": "graph",
        "classes": [
          {"name": "Code", "extends": "V"},
          {"name": "Country", "extends": "V"},
          {"name": "Has", "extends": "E"}
       ],
     "indexes": [{"class":"Code", "fields":["code:integer","in:any","out:any"], "type":"UNIQUE_HASH_INDEX" }]
    }
  }
}

but duplicated edges are created anyway.