Strings ending in backslash cause exceptions

[aroben]

define foo::test() {
  $a = 'string ending in \\'
}

Run puppet-lint on that and you'll get an exception:

puppet-lint-0.2.1/bin/../lib/puppet-lint/lexer.rb:130:in `tokenise': undefined method `[]' for nil:NilClass (NoMethodError)
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/../lib/puppet-lint/plugin.rb:38:in `load_data'
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/../lib/puppet-lint/plugin.rb:44:in `run'
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/../lib/puppet-lint.rb:143:in `run'
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/../lib/puppet-lint/bin.rb:102:in `run'
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/../lib/puppet-lint/bin.rb:99:in `each'
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/../lib/puppet-lint/bin.rb:99:in `run'
    from /Users/aroben/github/puppet/vendor/gems/ruby/1.8/gems/puppet-lint-0.2.1/bin/puppet-lint:7
    from bin/puppet-lint:12:in `load'
    from bin/puppet-lint:12