checkFormat raises exception for workflow input set by default to Null

[michael-kotliar]

Expected Behavior

When optional workflow input input_file with a format field is not provided and the default: null is used the checkFormat function shouldn't raise exception when trying to check format for this input.

Actual Behavior

checkFormat function raises exception for optional workflow input with default: null and format fields.
Workflow doesn't fail if:

• remove either default: null or format
• remove namespaces and schemas sections

Workflow Code

cwlVersion: v1.0
class: Workflow

inputs:
  input_file:
    type: File?
    default: null
    format: "http://edamontology.org/format_2572"

outputs: []

steps:
  cat:
    run: cat.cwl
    in:
      input_file: input_file
    out: []

$namespaces:
  s: http://schema.org/
$schemas:
- http://schema.org/docs/schema_org_rdfa.html
s:name: "workflow"

cwlVersion: v1.0
class: CommandLineTool

hints:
  DockerRequirement:
    dockerPull: ubuntu

inputs:
  input_file:
    type:
      - "null"
      - File
    inputBinding:
      position: 1

outputs: []

baseCommand: cat

Full Traceback

cwltool --debug workflow.cwl
/usr/local/bin/cwltool 1.0.20170525215327
Resolved 'workflow.cwl' to 'file:///Users/kot4or/workspaces/cwl_ws/cwl_sandbox/null_default_2/workflow.cwl'
No handlers could be found for logger "rdflib.term"
Parsed job order from command line: {
    "id": "workflow.cwl", 
    "input_file": null
}
Got workflow error
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/cwltool/main.py", line 243, in single_job_executor
    for r in jobiter:
  File "/usr/local/lib/python2.7/site-packages/cwltool/workflow.py", line 534, in job
    builder = self._init_job(job_order, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/cwltool/process.py", line 559, in _init_job
    checkFormat(builder.job[d], builder.do_eval(i["format"]), self.formatgraph)
  File "/usr/local/lib/python2.7/site-packages/cwltool/process.py", line 346, in checkFormat
    if "format" not in af:
TypeError: argument of type 'NoneType' is not iterable
Workflow error, try again with --debug for more information:
argument of type 'NoneType' is not iterable
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/cwltool/main.py", line 774, in main
    **vars(args))
  File "/usr/local/lib/python2.7/site-packages/cwltool/main.py", line 255, in single_job_executor
    raise WorkflowException(Text(e))
WorkflowException: argument of type 'NoneType' is not iterable

Your Environment

• cwltool version: 1.0.20170525215327

Link to replicate test

https://github.com/michael-kotliar/cwl_sandbox/tree/master/null_default_2