Error running brew upgrade

gistfile1.sh

Beor:web matt$ brew doctor
Your system is raring to brew.
Beor:web matt$ brew update
Initialized empty Git repository in /usr/local/.git/
remote: Counting objects: 48129, done.
remote: Compressing objects: 100% (21364/21364), done.
remote: Total 48129 (delta 30245), reused 41934 (delta 26093)
Receiving objects: 100% (48129/48129), 6.87 MiB | 1.00 MiB/s, done.
Resolving deltas: 100% (30245/30245), done.
From https://github.com/mxcl/homebrew
 * [new branch]      gh-pages   -> origin/gh-pages
 * [new branch]      master     -> origin/master
HEAD is now at cbcaa4d gpac: make lowercasing binaries an option
Already up-to-date.
Beor:web matt$ brew outdated
ack (1.94 < 1.96)
cmake (2.8.5 < 2.8.6)
gdbm (1.8.3 < 1.9.1)
git (1.7.6 < 1.7.7.3)
mongodb (1.8.2-x86_64 < 2.0.1-x86_64)
mysql (5.5.14 < 5.5.15)
oniguruma (5.9.1 < 5.9.2)
pngcrush (1.7.13 < 1.7.17)
redis (2.2.12 < 2.4.2)
sqlite (3.7.7 < 3.7.7.1)
Beor:web matt$ brew upgrade
Error: undefined method `include?' for nil:NilClass
Please report this bug:
    https://github.com/mxcl/homebrew/wiki/checklist-before-filing-a-new-issue
/usr/local/Library/Homebrew/formula.rb:393:in `canonical_name'
/usr/local/Library/Homebrew/formula.rb:425:in `factory'
/usr/local/Library/Contributions/examples/brew-upgrade.rb:7
/usr/local/Library/Contributions/examples/brew-upgrade.rb:7:in `map'
/usr/local/Library/Contributions/examples/brew-upgrade.rb:7
/usr/local/bin/brew:47:in `require'
/usr/local/bin/brew:47:in `require?'
/usr/local/bin/brew:80
# installing the outdated formula manually with `brew install` worked fine