Confusing error message when specifying a file improperly

[psaffrey-illumina]

Given this CWL:

class: CommandLineTool
cwlVersion: v1.0

inputs:
  pattern:
    type: string
    inputBinding: {position: 0}
  infile:
    type: File
    inputBinding: {position: 1}

outputs:
  outfile:
    type: stdout

baseCommand: grep

and this input:

infile: testfile.txt
pattern: Requirement

run with this cwltool:

$ cwltool --version
/usr/local/bin/cwltool 1.0.20161216212910

I get this:

Got workflow error
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/cwltool/main.py", line 225, in single_job_executor
    for r in jobiter:
  File "/Library/Python/2.7/site-packages/cwltool/draft2tool.py", line 243, in job
    builder = self._init_job(joborder, **kwargs)
  File "/Library/Python/2.7/site-packages/cwltool/process.py", line 445, in _init_job
    validate.validate_ex(self.names.get_name("input_record_schema", ""), builder.job)
  File "/Library/Python/2.7/site-packages/schema_salad/validate.py", line 267, in validate_ex
    f.name, indent(str(v)))))
  File "/Library/Python/2.7/site-packages/schema_salad/sourceline.py", line 152, in makeError
    lead = "%s:%i:%i:" % (self.item.lc.filename,
AttributeError: 'LineCol' object has no attribute 'filename'

the problem is that the file entry should not be specified as a string, it should be specified with the proper class, like this:

infile: 
  class: File
  path: test_file_one.txt
pattern: Requirement

but the error message does not provide very useful guidance on fixing this.