Issue installing after Ctrl-C vagrant

[Tonkpils]

I was attempting to install vagrant but it seemed to hang at 100%. I Ctrl-C and attempted to re-install and received this message.

$ brew cask install vagrant
==> Downloading https://dl.bintray.com/mitchellh/vagrant/vagrant_1.7.2.dmg
Already downloaded: /Library/Caches/Homebrew/vagrant-1.7.2.dmg
Error: no implicit conversion of nil into String
Please report this bug:
    https://github.com/caskroom/homebrew-cask/issues
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/digest.rb:44:in `initialize'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/digest.rb:44:in `open'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/digest.rb:44:in `file'
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/digest.rb:29:in `file'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/download.rb:41:in `block in _check_sums'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/download.rb:39:in `each'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/download.rb:39:in `_check_sums'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/download.rb:32:in `perform'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/installer.rb:72:in `download'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/installer.rb:49:in `install'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/cli/install.rb:20:in `block in install_casks'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/cli/install.rb:17:in `each'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/cli/install.rb:17:in `install_casks'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/cli/install.rb:6:in `run'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/cli.rb:81:in `run_command'
/usr/local/Cellar/brew-cask/0.44.0/rubylib/cask/cli.rb:121:in `process'
/usr/local/bin/brew-cask.rb:42:in `<top (required)>'

[tapeinosyne]

You are running an old version of homebrew-cask, which is affected by #7946. Upgrading should fix the issue:

brew update && brew upgrade brew-cask && brew cleanup && brew cask cleanup