RVM Error with gemset

gistfile1.txt

#!/usr/bin/env ruby
require 'rubygems'
require 'rvm'
require 'trollop'

opts = Trollop::options do
  opt :ruby, "ruby interp to use", :type => :string, :required => true
  opt :gem_name, "gem", :type => :string, :required => true
  opt :gem_version, "gem", :type => :string, :required => true
end

Trollop.die :ruby, "ruby #{opts[:ruby]} not found." unless RVM.list.rubies.include?(opts[:ruby])

RVM.use(opts[:ruby])

# create empty gemset
gemset_name = "#{opts[:ruby]}:#{opts[:gem_name]}:#{opts[:gem_version]}"
RVM.gemset_create(gemset_name)
RVM.gemset_use(gemset_name)

# raises:
# /Users/mnielsen/.rvm/gems/ruby-1.9.3-preview1/gems/rvm-1.11.3.3/lib/rvm/environment/utility.rb:36:in `identifier_to_gemset_name': undefined method `gsub' for nil:NilClass (NoMethodError)
	from /Users/mnielsen/.rvm/gems/ruby-1.9.3-preview1/gems/rvm-1.11.3.3/lib/rvm/environment/gemset.rb:86:in `gemset_use'
	from /Users/mnielsen/.rvm/gems/ruby-1.9.3-preview1/gems/rvm-1.11.3.3/lib/rvm.rb:149:in `method_missing'
	from ./reboot.rb:25:in `<main>'