浏览api.github，我看到的每个用户，gravatar_id值都是空的。
回复数据：
URL https://api.github.com/users/angular
RES
{
"login": "angular",
"id": 139426,
"avatar_url": "https://avatars.githubusercontent.com/u/139426?v=3",
"gravatar_id": "",
"url": "https://api.github.com/users/angular",
"html_url": "https://github.com/angular",
"followers_url": "https://api.github.com/users/angular/followers",
"following_url": "https://api.github.com/users/angular/following{/other_user}",
"gists_url": "https://api.github.com/users/angular/gists{/gist_id}",
"starred_url": "https://api.github.com/users/angular/starred{/owner}{/repo}",
"subscriptions_url": "https://api.github.com/users/angular/subscriptions",
"organizations_url": "https://api.github.com/users/angular/orgs",
"repos_url": "https://api.github.com/users/angular/repos",
"events_url": "https://api.github.com/users/angular/events{/privacy}",
"received_events_url": "https://api.github.com/users/angular/received_events",
"type": "Organization",
"site_admin": false,
"name": "Angular",
"company": null,
"blog": "angularjs.org",
"location": "",
"email": null,
"hireable": null,
"bio": null,
"public_repos": 95,
"public_gists": 0,
"followers": 0,
"following": 0,
"created_at": "2009-10-13T22:16:19Z",
"updated_at": "2015-04-12T01:40:18Z"
}
该值为空。