```coffeescript
###
#    Copyright 2015-2017 ppy Pty. Ltd.
#
#    This file is part of osu!web. osu!web is distributed with the hope of
#    attracting more community contributions to the core ecosystem of osu!.
#
#    osu!web is free software: you can redistribute it and/or modify
#    it under the terms of the Affero GNU General Public License version 3
#    as published by the Free Software Foundation.
#
#    osu!web is distributed WITHOUT ANY WARRANTY; without even the implied
#    warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#    See the GNU Affero General Public License for more details.
#
#    You should have received a copy of the GNU Affero General Public License
#    along with osu!web.  If not, see <http://www.gnu.org/licenses/>.
###

{div} = ReactDOMFactories

bn = 'avatar'

@UserAvatar = (props) ->
  modifiers = props
    .modifiers
    .map (m) => "#{bn}--#{m}"
    .join ' '

  className = "#{bn} #{modifiers}"

  if props.user.id?
    div
      className: className
      style:
        backgroundImage: "url('#{props.user.avatar_url}')"
  else
    div className: "#{className} #{bn}--guest"
```

Update UserAvatar to use bem helper
user
```coffeescript
###
#    Copyright 2015-2017 ppy Pty. Ltd.
#
#    This file is part of osu!web. osu!web is distributed with the hope of
#    attracting more community contributions to the core ecosystem of osu!.
#
#    osu!web is free software: you can redistribute it and/or modify
#    it under the terms of the Affero GNU General Public License version 3
#    as published by the Free Software Foundation.
#
#    osu!web is distributed WITHOUT ANY WARRANTY; without even the implied
#    warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#    See the GNU Affero General Public License for more details.
#
#    You should have received a copy of the GNU Affero General Public License
#    along with osu!web.  If not, see <http://www.gnu.org/licenses/>.
###

{div} = ReactDOMFactories

bn = 'avatar'

@UserAvatar = (props) ->
  if props.user.id?
    div
      className: osu.classWithModifiers(bn, props.modifiers)
      style:
        backgroundImage: "url('#{props.user.avatar_url}')"
  else
    div className: "#{className} #{bn}--guest"
```
assistant