Error when installing SourceTree package

[Gr1N]

% brew cask install sourcetree
==> Caveats
Cask sourcetree installs files under "/usr/local".  The presence of such
files can cause warnings when running "brew doctor", which is considered
to be a bug in homebrew-cask.

==> Downloading https://downloads.atlassian.com/software/sourcetree/SourceTree_2
Already downloaded: /Library/Caches/Homebrew/sourcetree-2.0.3.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/0.49.0/rubylib/cask/download.rb:40:in `block in _check_sums'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/download.rb:38:in `each'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/download.rb:38:in `_check_sums'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/download.rb:31:in `perform'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/installer.rb:74:in `download'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/installer.rb:51:in `install'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/cli/install.rb:20:in `block in install_casks'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/cli/install.rb:17:in `each'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/cli/install.rb:17:in `install_casks'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/cli/install.rb:6:in `run'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/cli.rb:81:in `run_command'
/usr/local/Cellar/brew-cask/0.49.0/rubylib/cask/cli.rb:121:in `process'
/usr/local/bin/brew-cask.rb:42:in `<top (required)>'
/Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require'
/usr/local/Library/brew.rb:59:in `require?'
/usr/local/Library/brew.rb:142:in `<main>'

[rolandwalker]

Hi!

This is a duplicate of #7946.

We recently merged a fix and cut release v0.50.0. The following command should fix the issue:

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

[Gr1N]

Thnx!