How to create spotify playlist dynamically? How to get "Spotify track id" from dynamic/next call?

I want to create dynamic playlist of spotify tracks. Currently I am using

1. Create dynamic playlist : http://developer.echonest.com/api/v4/playlist/dynamic/create?api_key=TAFYO7QHYKWQE791F&artist=akon

2. Call next song Api : http://developer.echonest.com/api/v4/playlist/dynamic/next?api_key=TAFYO7QHYKWQE791F&format=json&session_id=09d56ac060de45999c0dc09d8769d4e9

3. Get spotify trackId : http://developer.echonest.com/api/v4/song/profile?api_key=TAFYO7QHYKWQE791F&format=json&bucket=tracks&bucket=id:spotify-WW&id=SOMDLKR142C46A6648

But for few artists the tracks array returns nil value.

Please tell the correct way to do this.

Thanks.