[18.09] Don't attempt len(None), ensure stdout/stderr are strings in Job(Like).set_streams().

[natefoo]

Pulsar jobs that finish ok but with no stdout are failing with the following exception on usegalaxy.org:

Traceback (most recent call last):
  File "/cvmfs/main.galaxyproject.org/galaxy/lib/galaxy/jobs/runners/pulsar.py", line 514, in finish_job
    remote_metadata_directory=remote_metadata_directory,
  File "/cvmfs/main.galaxyproject.org/galaxy/lib/galaxy/jobs/__init__.py", line 1445, in finish
    job.set_streams(job.stdout, job.stderr)
  File "/cvmfs/main.galaxyproject.org/galaxy/lib/galaxy/model/__init__.py", line 227, in set_streams
    if (len(stdout) > galaxy.util.DATABASE_MAX_STRING_SIZE):
TypeError: object of type 'NoneType' has no len()

Possibly due to #6565 although I'm not sure how exactly.

[dannon]

Might read cleaner to set default parameters on the function, any reason not to do that?

(Does unicodify return None for empty strings, instead of an empty unicode string? That's the only reason I could think of)

[nsoranzo]

unicodify() returns None for None, not for ''

[dannon]

@nsoranzo Got it, yeah. I just realized my suggestion probably didn't make sense, but that's what I was getting at -- instead of having the logic in consumers like this it might be good to standardize behavior at a single point. That's for future refactoring though, I guess, no worries about it here.

[natefoo]

@martenson Thanks!