Get Category's Playlists API returns null entry

[aome510]

Originally reported in aome510/spotify-player#821.

I observed that when calling the get-a-categories-playlists API on some categories, the following entry will be returned in the playlists list:

{
  "collaborative": false,
  "description": null,
  "external_urls": {
    "spotify": "https://open.spotify.com/playlist/null"
  },
  "href": "https://api.spotify.com/v1/playlists/null",
  "id": null,
  "images": [
    {
      "height": null,
      "url": null,
      "width": null
    }
  ],
  "name": null,
  "owner": {
    "display_name": null,
    "external_urls": {
      "spotify": "https://open.spotify.com/user/null"
    },
    "href": "https://api.spotify.com/v1/users/null",
    "id": null,
    "type": "user",
    "uri": null
  },
  "primary_color": null,
  "public": true,
  "snapshot_id": null,
  "tracks": {
    "href": "https://api.spotify.com/v1/playlists/null/tracks",
    "total": null
  },
  "type": "playlist",
  "uri": null
},

For example, I ran

curl --request GET \
      --url https://api.spotify.com/v1/browse/categories/0JQ5DAqbMKFQ00XGBls6ym/playlists \
      --header 'Authorization: Bearer $TOKEN"

and got a response as follows

{"message":"Hip-Hop","playlists":{"href":"https://api.spotify.com/v1/browse/categories/0JQ5DAqbMKFQ00XGBls6ym/playlists?offset=0&limit=20","items":[{"collaborative":false,"description":"The coldest sounds in hip-hop, coming out of Canada. Cover: \nSavv4x","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX59ogDi1Z2XL"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX59ogDi1Z2XL","id":"37i9dQZF1DX59ogDi1Z2XL","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f000000027b331b5481197322cb34cba9","width":null}],"name":"Northern Bars","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAFiEqZluryD/sP3u29/F1MnRPKOH","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX59ogDi1Z2XL/tracks","total":75},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX59ogDi1Z2XL"},{"collaborative":false,"description":"Today's Hip-Hop with Drake, Offset, Gunna, Bryson Tiller, Lithe and Travis Scott.","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWY6tYEFs22tT"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWY6tYEFs22tT","id":"37i9dQZF1DWY6tYEFs22tT","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002152e989db18a8105bfbd6372","width":null}],"name":"Hip-Hop Central","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAF/MW3KJus0A0vHo059wGaQNb4er","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWY6tYEFs22tT/tracks","total":49},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWY6tYEFs22tT"},{"collaborative":false,"description":"The latest hip-hop, refreshed weekly. Cover: Lithe","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWV1aMSQY91oR"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWV1aMSQY91oR","id":"37i9dQZF1DWV1aMSQY91oR","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002cd654722fda36b6fad3e760a","width":null}],"name":"New Hip-Hop","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAACZGepcql/8D3rrJxOpwPDwXVuYx","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWV1aMSQY91oR/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWV1aMSQY91oR"},{"collaborative":false,"description":"The tracks you just keep pulling up. Cover: Travis Scott","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX48TTZL62Yht"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX48TTZL62Yht","id":"37i9dQZF1DX48TTZL62Yht","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f0000000224db992dbb2f15bde5bb5573","width":null}],"name":"Hip-Hop Favourites","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAMYAPn95YdUZOlrWhje0nD1EBkZX","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX48TTZL62Yht/tracks","total":100},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX48TTZL62Yht"},{"collaborative":false,"description":"Laid back cratedigger hip-hop from around the world.","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX8Kgdykz6OKj"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX8Kgdykz6OKj","id":"37i9dQZF1DX8Kgdykz6OKj","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f000000028e709fabcdb701b300bf5684","width":null}],"name":"Jazz Rap","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAOesjxr2NFYoKVw43UQ3IQNm08oq","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX8Kgdykz6OKj/tracks","total":100},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX8Kgdykz6OKj"},{"collaborative":false,"description":"Le meilleur du hip-hop québécois. Photo: MB, Souldia, White-B, Lost","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWTZeTXqKTge4"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWTZeTXqKTge4","id":"37i9dQZF1DWTZeTXqKTge4","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f000000025381b34a39101bd7e8cfc61b","width":null}],"name":"Rap québ","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAJR09KV6+KhrUQyXPFWqNMthz0PR","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWTZeTXqKTge4/tracks","total":78},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWTZeTXqKTge4"},{"collaborative":false,"description":"The coldest sounds in hip-hop, coming out of Canada. Cover: \nSavv4x","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX59ogDi1Z2XL"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX59ogDi1Z2XL","id":"37i9dQZF1DX59ogDi1Z2XL","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f000000027b331b5481197322cb34cba9","width":null}],"name":"Northern Bars","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAFiEqZluryD/sP3u29/F1MnRPKOH","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX59ogDi1Z2XL/tracks","total":75},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX59ogDi1Z2XL"},{"collaborative":false,"description":"The Best of Hip-Hop, Rap and Drill from the UK. Cover: Fredo","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX6PKX5dyBKeq"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX6PKX5dyBKeq","id":"37i9dQZF1DX6PKX5dyBKeq","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002d8402123a1743e70d942b3a3","width":null}],"name":"Rap UK","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAKH/tSvxvqDFpQrcFbgMyt8V+COc","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX6PKX5dyBKeq/tracks","total":70},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX6PKX5dyBKeq"},{"collaborative":false,"description":"New music from Yeat, Eminem and Key Glock. ","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX0XUsuxWHRQd"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX0XUsuxWHRQd","id":"37i9dQZF1DX0XUsuxWHRQd","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002f0f239d143d4384ea33f0aa2","width":null}],"name":"RapCaviar","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#F49B23","public":true,"snapshot_id":"AAAAAAggdzjKS7H1PD6xbWm/008tRYyF","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX0XUsuxWHRQd/tracks","total":51},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX0XUsuxWHRQd"},{"collaborative":false,"description":"The official voice of the next generation. Cover: <a href=\"spotify:artist:31xNxPD0tnYKr7Krg8dyPB\">BunnaB</a> ","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX2RxBh64BHjQ"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX2RxBh64BHjQ","id":"37i9dQZF1DX2RxBh64BHjQ","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002ec7be5c45a54c212288105a6","width":null}],"name":"Most Necessary","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#F49B23","public":true,"snapshot_id":"AAAAAHnebRbe2eBnH3PcAdi6o+NBviM3","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX2RxBh64BHjQ/tracks","total":100},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX2RxBh64BHjQ"},{"collaborative":false,"description":"Damn son, where'd ya find this? ","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX3XgesiUXnsq"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX3XgesiUXnsq","id":"37i9dQZF1DX3XgesiUXnsq","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002e535ea21f1f09aee95c36386","width":null}],"name":"Raw & Uncut","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAErPVsZpSQda721nqdHIKjQaKqvc","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX3XgesiUXnsq/tracks","total":75},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX3XgesiUXnsq"},{"collaborative":false,"description":"Taking it way back! When hip-hop meets jazz. Fusion and samples. Cover: Jeezy","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWVA1Gq4XHa6U"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWVA1Gq4XHa6U","id":"37i9dQZF1DWVA1Gq4XHa6U","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002b3cba5e03021666006c8a2eb","width":null}],"name":"Gold School","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAPDcWA78bhJCASMwkiLxivteT++Q","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWVA1Gq4XHa6U/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWVA1Gq4XHa6U"},{"collaborative":false,"description":"Real rap music from the golden era.\n","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX186v583rmzp"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX186v583rmzp","id":"37i9dQZF1DX186v583rmzp","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f000000028908106e49cde03e6d67073e","width":null}],"name":"I Love My '90s Hip-Hop","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAChXs9VqbRXwXVCgdidO3sD2ombm","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX186v583rmzp/tracks","total":100},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX186v583rmzp"},{"collaborative":false,"description":"The south got something to say. Cover: Gucci Mane","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWYok9l1JL7GM"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWYok9l1JL7GM","id":"37i9dQZF1DWYok9l1JL7GM","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002f8fc7dba058be88715fcdef9","width":null}],"name":"Down South Classics","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#FFFFFF","public":true,"snapshot_id":"AAAAABnfZhOL3VWjbKNtjeftCM7XSiTz","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWYok9l1JL7GM/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWYok9l1JL7GM"},{"collaborative":false,"description":"The best side! Cover: The Game","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX9sQDbOMReFI"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX9sQDbOMReFI","id":"37i9dQZF1DX9sQDbOMReFI","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002b0d16e2c25bcd98d133e63aa","width":null}],"name":"West Coast Classics","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#FFFFFF","public":true,"snapshot_id":"AAAAAPIVvo4Kswf1AofG4DtfzufMHznw","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX9sQDbOMReFI/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX9sQDbOMReFI"},{"collaborative":false,"description":null,"external_urls":{"spotify":"https://open.spotify.com/playlist/null"},"href":"https://api.spotify.com/v1/playlists/null","id":null,"images":[{"height":null,"url":null,"width":null}],"name":null,"owner":{"display_name":null,"external_urls":{"spotify":"https://open.spotify.com/user/null"},"href":"https://api.spotify.com/v1/users/null","id":null,"type":"user","uri":null},"primary_color":null,"public":true,"snapshot_id":null,"tracks":{"href":"https://api.spotify.com/v1/playlists/null/tracks","total":null},"type":"playlist","uri":null},{"collaborative":false,"description":"Where it all started. Cover: Jadakiss","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWYGxBNe4qojI"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWYGxBNe4qojI","id":"37i9dQZF1DWYGxBNe4qojI","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002d5b51fcfd90aa9d4cc07127f","width":null}],"name":"I Love My East Coast Classics","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#FFFFFF","public":true,"snapshot_id":"AAAAAPuXciK5Jy9YQaMf4NmOdONzZUTE","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWYGxBNe4qojI/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWYGxBNe4qojI"},{"collaborative":false,"description":"It's a Midwest thing. Cover: Bone Thugs-n-Harmony","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DWTJzNR1J5ygQ"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWTJzNR1J5ygQ","id":"37i9dQZF1DWTJzNR1J5ygQ","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f00000002f4505a255e515d4919314995","width":null}],"name":"I Love My Midwest Classics","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#FFFFFF","public":true,"snapshot_id":"AAAAALwAp+sKDKs0Clqyy69wstNiiCkI","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DWTJzNR1J5ygQ/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DWTJzNR1J5ygQ"},{"collaborative":false,"description":"Essential songs from the late '90s, early 2000s underground hip-hop scene. Cover: Mos Def","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DXdUAMxTn0rVu"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DXdUAMxTn0rVu","id":"37i9dQZF1DXdUAMxTn0rVu","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f0000000272e5f378789483698a67c620","width":null}],"name":"I Love My Underground Classics","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#ffffff","public":true,"snapshot_id":"AAAAAM0a5i3KCW5uc01ZYv5i1MZQsDcA","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DXdUAMxTn0rVu/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DXdUAMxTn0rVu"},{"collaborative":false,"description":"Classics from trailblazing women in hip-hop. Cover: Trina","external_urls":{"spotify":"https://open.spotify.com/playlist/37i9dQZF1DX9iGsUcr0Bpa"},"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX9iGsUcr0Bpa","id":"37i9dQZF1DX9iGsUcr0Bpa","images":[{"height":null,"url":"https://i.scdn.co/image/ab67706f0000000245bf19b3a44fe446e50269bd","width":null}],"name":"Door Knockers","owner":{"display_name":"Spotify","external_urls":{"spotify":"https://open.spotify.com/user/spotify"},"href":"https://api.spotify.com/v1/users/spotify","id":"spotify","type":"user","uri":"spotify:user:spotify"},"primary_color":"#FFFFFF","public":true,"snapshot_id":"AAAAACKk5mvrMSqjgCNaW+f1kyJEv9tR","tracks":{"href":"https://api.spotify.com/v1/playlists/37i9dQZF1DX9iGsUcr0Bpa/tracks","total":50},"type":"playlist","uri":"spotify:playlist:37i9dQZF1DX9iGsUcr0Bpa"}],"limit":20,"next":"https://api.spotify.com/v1/browse/categories/0JQ5DAqbMKFQ00XGBls6ym/playlists?offset=20&limit=20","offset":0,"previous":null,"total":75}}

NOTE: the playlist list might change everyday and might be different for each person, so the issue might be reproducible for me but not for others.

[ramsayleung]

I can re-produce the issue by the given test data:

#[test]
#[wasm_bindgen_test]
fn test_null_playlist() {
    let json = r#"
{
  "collaborative": false,
  "description": null,
  "external_urls": {
    "spotify": "https://open.spotify.com/playlist/null"
  },
  "href": "https://api.spotify.com/v1/playlists/null",
  "id": null,
  "images": [
    {
      "height": null,
      "url": null,
      "width": null
    }
  ],
  "name": null,
  "owner": {
    "display_name": null,
    "external_urls": {
      "spotify": "https://open.spotify.com/user/null"
    },
    "href": "https://api.spotify.com/v1/users/null",
    "id": null,
    "type": "user",
    "uri": null
  },
  "primary_color": null,
  "public": true,
  "snapshot_id": null,
  "tracks": {
    "href": "https://api.spotify.com/v1/playlists/null/tracks",
    "total": null
  },
  "type": "playlist",
  "uri": null
},
"#;
    let playlist: SimplifiedArtist = deserialize(json);
    assert!(playlist.href.unwrap().len() > 0)
}

---- test_null_playlist stdout ----
from_str

thread 'test_null_playlist' panicked at tests/test_models.rs:1419:38:
called `Result::unwrap()` on an `Err` value: Error("invalid type: null, expected a string", line: 17, column: 14)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

the problem is that:

1. href is defined as String but JSON has null
2. id is defined as PlaylistId<'static> but JSON has null
3. name is defined as String but JSON has null
4. snapshot_id is defined as String but JSON has null

It just gives an impression that almost all the fields are nullable, and the doc doesn't tell which field is required and which field is nullable as well.