octopose generate fails with no projects specified

[george-ayris]

octopose generate -p Tasks works as expected.

octopose generate now gives the error:

Traceback (most recent call last):
  File "D:\dev\octopose-testing\env\Scripts\octopose-script.py", line 9, in <module>
    load_entry_point('octopose==0.1.2', 'console_scripts', 'octopose')()
  File "d:\dev\octopose-testing\env\lib\site-packages\octopose\octopose.py", line 35, in main
    generate_manifest.main()
  File "d:\dev\octopose-testing\env\lib\site-packages\octopose\generate_manifest.py", line 61, in main
    if required_to_deploy_this_project(project, specific_projects):
  File "d:\dev\octopose-testing\env\lib\site-packages\octopose\generate_manifest.py", line 33, in required_to_deploy_this_project
    return len(specific_projects) == 0 or project in specific_projects
TypeError: object of type 'NoneType' has no len()