Blame applied on empty file gives 500

Created by: byo

Here's the content of a log file:

Processing by BlameController#show as HTML
  Parameters: {"project_id"=>"micazook_vikings_flashfrontend", "id"=>"master/empty.txt"}
  Rendered shared/_ref_switcher.html.haml (3.1ms)
  Rendered shared/_clone_panel.html.haml (0.3ms)
  Rendered blame/_head.html.haml (4.2ms)
  Rendered tree/_blob_actions.html.haml (2.9ms)
  Rendered blame/show.html.haml within layouts/project_resource (9.3ms)
Completed 500 Internal Server Error in 155ms

ActionView::Template::Error (Commit#author delegated to commit.author, but commit is nil: #<Commit:0x00000007824658 @commit=nil, @head=nil>):
    24:           - commit = Commit.new(commit)
    25:           - commit = CommitDecorator.decorate(commit)
    26:           %tr
    27:             %td.author= commit.author_link avatar: true, size: 16
    28:             %td.blame_commit
    29:               &nbsp;
    30:               %code= link_to commit.short_id, project_commit_path(@project, commit)
  app/models/commit.rb:16:in `rescue in author'
  app/models/commit.rb:13:in `author'
  app/models/commit.rb:122:in `author_name'
  app/decorators/commit_decorator.rb:76:in `person_link'
  app/decorators/commit_decorator.rb:53:in `author_link'
  app/views/blame/show.html.haml:27:in `block in _app_views_blame_show_html_haml__4514273325856906551_40796020'
  app/views/blame/show.html.haml:23:in `each'
  app/views/blame/show.html.haml:23:in `_app_views_blame_show_html_haml__4514273325856906551_40796020'