I'm trying to build a rubygem, but I keep getting the following error. 
Can anybody help?

$ gem build wordnet.gemspec 
ERROR:  While executing gem ... (NoMethodError)
    undefined method `empty?' for nil:NilClass

$ cat wordnet.gemspec 
Gem::Specification.new do |s|
  s.name="WordNet"
  s.author="Ken Bloom"
  s.email="kbloom / gmail.com"
  s.version="1.0.1"
  s.summary="A binding to the WordNet C library"
  s.require_path="ext"
  
  #disabled because it spews lots of errors
  #but the generated rdoc isn't useful in the least
  s.has_rdoc=false 

  s.files += Dir["ext/*"]
  s.extensions << "ext/extconf.rb"
end

$ gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.2
  - RUBY VERSION: 1.8.7 (2008-08-11 patchlevel 72) [x86_64-linux]
  - INSTALLATION DIRECTORY: /var/lib/gems/1.8
  - RUBY EXECUTABLE: /usr/bin/ruby1.8
  - EXECUTABLE DIRECTORY: /var/lib/gems/1.8/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /var/lib/gems/1.8
     - /home/bloom/.gem/ruby/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://gems.rubyforge.org/

-- 
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/