gem generate_index fails after yard install

We installed yard 0.6.8 and now gem generate_index fails in ways that it did not before. I thought maybe it was my own gemspecs to blame, but I tried with activesupport-3.0.7.gem. Not sure if that's a reasonable test gem.

This may be a yard problem rather than a rubygems problem, looking possible for a workaround on the gem side, maybe to disable hooks into yard?

$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.7.2
  - RUBY VERSION: 1.9.2 (2011-02-18 patchlevel 180) [x86_64-linux]
  - INSTALLATION DIRECTORY: /opt/ruby-1.9.2-p180/lib/ruby/gems/1.9.1
  - RUBY EXECUTABLE: /opt/ruby-1.9.2-p180/bin/ruby
  - EXECUTABLE DIRECTORY: /opt/ruby-1.9.2-p180/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /opt/ruby-1.9.2-p180/lib/ruby/gems/1.9.1
     - /opt/home/DJacqu001/.gem/ruby/1.9.1
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://rubygems.org/

$ gem generate_index
Loading 1 gems from .
.
Loaded all gems
loaded: 0.028s
Generating Marshal quick index gemspecs for 1 gems
ERROR:  While executing gem ... (TypeError)
    can't convert nil into String

$ gem generate_index --debug
Exception `NameError' at /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:163 - uninitialized constant Gem::Commands::GenerateIndexCommand
Exception `LoadError' at /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36 - no such file to load -- psych
Exception `LoadError' at /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:60 - no such file to load -- psych
Exception `Errno::ENOENT' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:1217 - No such file or directory - /tmp/gem_generate_index_12525
Exception `Errno::ENOENT' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:1217 - No such file or directory - /tmp/gem_generate_index_12525
Exception `Errno::ENOENT' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:1314 - No such file or directory - /tmp/gem_generate_index_12525
Exception `Errno::ENOENT' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:243 - No such file or directory - /tmp/gem_generate_index_12525/quick/Marshal.4.8
Exception `Errno::ENOENT' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:243 - No such file or directory - 
Exception `Errno::EEXIST' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:243 - File exists - /tmp
Exception `Errno::EEXIST' at /opt/ruby-1.9.2-p180/lib/ruby/1.9.1/fileutils.rb:243 - File exists - /tmp/gem_generate_index_12525
Loading 1 gems from .
Exception `NoMethodError' at /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/package/tar_input.rb:53 - undefined method `readpartial' for #<Gem::Package::TarReader::Entry:0x0000001cdf0e28>
Exception `NoMethodError' at /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:449 - undefined method `readpartial' for #<Gem::Package::TarReader::Entry:0x0000001cdf0e28>
Exception `IOError' at /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/format.rb:45 - closed stream
.
Loaded all gems
loaded: 0.027s
Generating Marshal quick index gemspecs for 1 gems
Exception `TypeError' at /opt/ruby-1.9.2-p180/lib/ruby/gems/1.9.1/gems/yard-0.6.8/lib/yard/rubygems/specification.rb:31 - can't convert nil into String
ERROR:  While executing gem ... (TypeError)
    can't convert nil into String
    /opt/ruby-1.9.2-p180/lib/ruby/gems/1.9.1/gems/yard-0.6.8/lib/yard/rubygems/specification.rb:31:in `[]='
    /opt/ruby-1.9.2-p180/lib/ruby/gems/1.9.1/gems/yard-0.6.8/lib/yard/rubygems/specification.rb:31:in `_dump_with_rdoc'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:167:in `dump'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:167:in `block (2 levels) in build_marshal_gemspecs'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:163:in `each'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:163:in `block in build_marshal_gemspecs'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems.rb:1115:in `time'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:162:in `build_marshal_gemspecs'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:128:in `build_indicies'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/indexer.rb:460:in `generate_index'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/commands/generate_index_command.rb:118:in `execute'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/command.rb:278:in `invoke'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:133:in `process_args'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:103:in `run'
    /opt/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/gem_runner.rb:64:in `run'
    /opt/ruby-1.9.2-p180/bin/gem:21:in `<main>'