undefined method `method_list' for nil:NilClass

When running gem server and trying to view rdoc for an installed gem (net-ldap-0.11, in my case), I get the following error page:

Error

While processing http://localhost:8808/doc_root/net-ldap-0.11/ the RDoc (4.2.0) server has encountered a NoMethodError exception:

undefined method `method_list' for nil:NilClass
Please report this to the RDoc issues tracker. Please include the RDoc version, the URI above and exception class, message and backtrace. If you're viewing a gem's documentation, include the gem name and version. If you're viewing Ruby's documentation, include the version of ruby.

Backtrace:

C:/Ruby193/lib/ruby/gems/1.9.1/gems/rdoc-4.2.0/lib/rdoc/store.rb:505:in block in load_all' C:/Ruby193/lib/ruby/gems/1.9.1/gems/rdoc-4.2.0/lib/rdoc/store.rb:500:ineach'
C:/Ruby193/lib/ruby/gems/1.9.1/gems/rdoc-4.2.0/lib/rdoc/store.rb:500:in load_all' C:/Ruby193/lib/ruby/gems/1.9.1/gems/rdoc-4.2.0/lib/rdoc/servlet.rb:182:indocumentation_source'
C:/Ruby193/lib/ruby/gems/1.9.1/gems/rdoc-4.2.0/lib/rdoc/servlet.rb:385:in show_documentation' C:/Ruby193/lib/ruby/gems/1.9.1/gems/rdoc-4.2.0/lib/rdoc/servlet.rb:125:indo_GET'
C:/Ruby193/lib/ruby/1.9.1/webrick/httpservlet/abstract.rb:106:in service' C:/Ruby193/lib/ruby/1.9.1/webrick/httpserver.rb:138:inservice'
C:/Ruby193/lib/ruby/1.9.1/webrick/httpserver.rb:94:in run' C:/Ruby193/lib/ruby/1.9.1/webrick/server.rb:191:inblock in start_thread'

Start with lib/rdoc/store.rb around load_all, using the reported net-ldap-0.11 URL through gem server to reproduce the failure. Trace how the RDoc server loads the gem documentation and verify that viewing the documentation no longer raises the reported NoMethodError.