undefined method `map' for nil:NilClass

[sooding]

on running this

$ rake gems:install

WARNING: 'require 'rake/rdoctask'' is deprecated. Please use 'require 'rdoc/task' (in RDoc 2.4.2+)' instead.
at /var/lib/gems/1.9.1/gems/rake-0.9.2.2/lib/rake/rdoctask.rb
rake aborted!
undefined method `map' for nil:NilClass

Tasks: TOP => environment
(See full trace by running task with --trace)