Homebrew: "Error: undefined method `<' for nil:NilClass"

gistfile1.txt

~ $ brew doctor
Error: undefined method `<' for nil:NilClass
Please report this bug:
    https://git.io/brew-troubleshooting
/usr/local/Library/Homebrew/os/mac/xcode.rb:131:in `provides_autotools?'
/usr/local/Library/Homebrew/diagnostic.rb:1038:in `check_for_autoconf'
/usr/local/Library/Homebrew/cmd/doctor.rb:30:in `block in doctor'
/usr/local/Library/Homebrew/cmd/doctor.rb:23:in `each'
/usr/local/Library/Homebrew/cmd/doctor.rb:23:in `doctor'
/usr/local/Library/brew.rb:143:in `<main>'
~ $ brew config
HOMEBREW_VERSION: 0.9.5
ORIGIN: https://github.com/Homebrew/homebrew
HEAD: d636716b20c88b8669cee4889019654075d06711
Last commit: 20 minutes ago
HOMEBREW_PREFIX: /usr/local
HOMEBREW_REPOSITORY: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
HOMEBREW_BOTTLE_DOMAIN: https://homebrew.bintray.com
CPU: 8-core 64-bit haswell
OS X: 10.11.2-x86_64
Xcode: N/A
CLT: N/A
Clang: N/A
X11: 2.7.8 => /opt/X11
System Ruby: 2.0.0-p645
Perl: /usr/bin/perl
Python: /usr/bin/python
Ruby: /Users/chuckhoffman/.rvm/rubies/ruby-2.1.0/bin/ruby
Java: 1.8.0_60, 1.7.0_55