Why song_hotttnesss is an array on some requests?

Take for example this request :

http://developer.echonest.com/api/v4/song/search?api_key=3AG7XTMTSROUMQKPY&format=json&results=100&bucket=audio_summary&bucket=artist_location&bucket=song_hotttnesss&bucket=id:deezer&artist_id=AR487ZS1187FB5C243&sort=song_hotttnesss-desc

I get these results : `{

"title": "Booty Swing",
"artist_name": "2B",
"artist_foreign_ids": [
    {
        "catalog": "deezer",
        "foreign_id": "deezer:artist:1885041"
    }
],
"song_hotttnesss": [
    0
],

`

As you can see, the song_hotttnesss is returned as an array, which makes my code crash.