empty.yml can't be quite empty..?
empty.yml can't be quite empty..?

Avoid bug:

```
Resolved 'expression.cwl' to 'file:///home/stain/src/cwl-test/expression.cwl'
Traceback (most recent call last):
  File "/home/stain/bin/cwl-runner", line 11, in <module>
    sys.exit(main())
  File "/home/stain/.local/lib/python2.7/site-packages/cwltool/main.py", line 701, in main
    fetcher_constructor=fetcher_constructor)
  File "/home/stain/.local/lib/python2.7/site-packages/cwltool/main.py", line 494, in load_job_order
    if "cwl:tool" in job_order_object:
TypeError: argument of type 'NoneType' is not iterable
```
stain/common-workflow-language,StarvingMarvin/common-workflow-language,StarvingMarvin/common-workflow-language,stain/common-workflow-language,ohsu-computational-biology/common-workflow-language,curoverse/common-workflow-language,hmenager/common-workflow-language,StarvingMarvin/common-workflow-language,ohsu-computational-biology/common-workflow-language,common-workflow-language/common-workflow-language,stain/common-workflow-language,StarvingMarvin/common-workflow-language,common-workflow-language/common-workflow-language,mr-c/common-workflow-language,common-workflow-language/common-workflow-language,hmenager/common-workflow-language,dleehr/common-workflow-language,mr-c/common-workflow-language,common-workflow-language/common-workflow-language,dleehr/common-workflow-language,ohsu-computational-biology/common-workflow-language,curoverse/common-workflow-language,dleehr/common-workflow-language,mr-c/common-workflow-language,stain/common-workflow-language,dleehr/common-workflow-language,hmenager/common-workflow-language,hmenager/common-workflow-language