UserStreamsの user_update イベントで source.listed_count が null になる

gistfile1.txt

{
  "created_at": "Sun Oct 12 08:29:05 +0000 2014",
  "event": "user_update",
  "source": {
    "contributors_enabled": false,
    "created_at": "Thu Aug 19 19:01:26 +0000 2010",
    "default_profile": false,
    "default_profile_image": true,
    "description": "https://t.co/SLFC3SuxO7 <>\"",
    "favourites_count": -1,
    "follow_request_sent": null,
    "followers_count": -1,
    "following": null,
    "friends_count": -1,
    "geo_enabled": false,
    "id": 180482916,
    "id_str": "180482916",
    "is_translation_enabled": false,
    "is_translator": false,
    "lang": "en",
    "listed_count": null,
    "location": "ここ",
    "name": "upsilon",
    "notifications": null,
    "profile_background_color": "CFEB81",
    "profile_background_image_url": null,
    "profile_background_image_url_https": null,
    "profile_background_tile": false,
    "profile_image_url": null,
    "profile_image_url_https": null,
    "profile_link_color": "999900",
    "profile_sidebar_border_color": "BDDCAD",
    "profile_sidebar_fill_color": "99FF99",
    "profile_text_color": "336666",
    "profile_use_background_image": false,
    "protected": true,
    "screen_name": "kim_upslion",
    "statuses_count": -1,
    "time_zone": "Tokyo",
    "url": "http://t.co/ouwcZ2Rp2a",
    "utc_offset": null,
    "verified": false
  },
  "target": {
    "contributors_enabled": false,
    "created_at": "Thu Aug 19 19:01:26 +0000 2010",
    "default_profile": false,
    "default_profile_image": true,
    "description": "https://t.co/SLFC3SuxO7 <>\"",
    "favourites_count": -1,
    "follow_request_sent": null,
    "followers_count": -1,
    "following": null,
    "friends_count": -1,
    "geo_enabled": false,
    "id": 180482916,
    "id_str": "180482916",
    "is_translation_enabled": false,
    "is_translator": false,
    "lang": "en",
    "listed_count": null,
    "location": "ここ",
    "name": "upsilon",
    "notifications": null,
    "profile_background_color": "CFEB81",
    "profile_background_image_url": null,
    "profile_background_image_url_https": null,
    "profile_background_tile": false,
    "profile_image_url": null,
    "profile_image_url_https": null,
    "profile_link_color": "999900",
    "profile_sidebar_border_color": "BDDCAD",
    "profile_sidebar_fill_color": "99FF99",
    "profile_text_color": "336666",
    "profile_use_background_image": false,
    "protected": true,
    "screen_name": "kim_upslion",
    "statuses_count": -1,
    "time_zone": "Tokyo",
    "url": "http://t.co/ouwcZ2Rp2a",
    "utc_offset": null,
    "verified": false
  }
}