ansible/ansible — pull request #1900 by bostrick (2013-01-23 18:58:15+00:00)
Title: protect PluginLoader._extra_dirs from appending None

PluginLoader.add_directory() can receive None from, for example,
Inventory.add_directory(self.basedir()) if host_list is a custom list.
None has no reasonable interpretation other than ignore it.