Create/Update Asset-Level data

I tried to create and update Asset-Level data with some "survey_data", but I got the following error:

{
    "error": "NoMethodError",
    "message": "undefined method `each_pair' for nil:NilClass",
    "backtrace": [
         // .....
    ]
}

I tried to send same request like in documentation:

{
  "buildings": [
    {
      "partners_id": "213412434",
      "asset_name": "The White House",
      "asset_address": "1600 Pennsylvania Avenue NW, Washington DC",
      "survey_data": {
        "2013": {
          "asset_own": 6,
          "en_man_bcf_abs": 50000,
          "en_man_bcf_cov": 1000,
          "en_man_bcf_tot": 1000
        },
        "2014": {
          "asset_own": 12,
          "en_man_bcf_abs": 100000,
          "en_man_bcf_cov": 1200,
          "en_man_bcf_tot": ""
        }
      }
    }
  ]
}

What have I missed?

GRESB / api-docs

Create/Update Asset-Level data #13