When installs non-globally from npm registry, list is nil initially when no package was installed locally

npm installation would fails with:

NoMethodError
-------------
undefined method `key?' for nil:NilClass

Cookbook Trace:
---------------
/var/chef/cache/cookbooks/nodejs/libraries/nodejs_helper.rb:36:in `npm_package_installed?'
/var/chef/cache/cookbooks/nodejs/providers/npm.rb:28:in `installed?'
/var/chef/cache/cookbooks/nodejs/providers/npm.rb:12:in `block (3 levels) in class_from_file'