{"action":"opened","issue":{"url":"https://api.github.com/repos/vuejs/vue/issues/4050","repository_url":"https://api.github.com/repos/vuejs/vue","labels_url":"https://api.github.com/repos/vuejs/vue/issues/4050/labels{/name}","comments_url":"https://api.github.com/repos/vuejs/vue/issues/4050/comments","events_url":"https://api.github.com/repos/vuejs/vue/issues/4050/events","html_url":"https://github.com/vuejs/vue/issues/4050","id":185836485,"number":4050,"title":"Transition class bind null values has DOMException in addClass function.","user":{"login":"sean220","id":2570572,"avatar_url":"https://avatars.githubusercontent.com/u/2570572?v=3","gravatar_id":"","url":"https://api.github.com/users/sean220","html_url":"https://github.com/sean220","followers_url":"https://api.github.com/users/sean220/followers","following_url":"https://api.github.com/users/sean220/following{/other_user}","gists_url":"https://api.github.com/users/sean220/gists{/gist_id}","starred_url":"https://api.github.com/users/sean220/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/sean220/subscriptions","organizations_url":"https://api.github.com/users/sean220/orgs","repos_url":"https://api.github.com/users/sean220/repos","events_url":"https://api.github.com/users/sean220/events{/privacy}","received_events_url":"https://api.github.com/users/sean220/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2016-10-28T04:30:00Z","updated_at":"2016-10-28T04:30:00Z","closed_at":null,"body":"### Vue.js version\r\n2.0.1\r\n\r\n````\r\n<transition :enter-active-class=\"animatedIn\" >\r\n````\r\nWhen 'animateIn' bind value is empty string or null,addClass function has exception:\r\n````\r\nvue.js:4540 Uncaught (in promise) DOMException: Failed to execute 'add' on 'DOMTokenList': The token provided must not be empty\r\n````\r\nSemantically,Binding a null value is intended to stop the transition effect.\r\nShould a null check be made in addClass function or the transition should be ignored in the case of null values?\r\n\r\n"}}
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