Unexpected behavior when analyzing images in parallel

[DannieSheng]

I was trying to analyzing a bunch of images in parallel. And things went on well until I add one line of code in my pipeline. That code is used to add observation to output class.
I have already added one observation, and the parallelization worked well, I was able to get my expected result. However, after I added another observation, the result cannot be processed, I got error message like this:

Processing results...
Traceback (most recent call last):
  File "/home/hsheng/miniconda3/envs/plantcv/bin/plantcv-workflow.py", line 4, in <module>
    __import__('pkg_resources').run_script('plantcv==3.11.0+3.gd86fe6b.dirty', 'plantcv-workflow.py')
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/site-packages/pkg_resources/__init__.py", line 665, in run_script
    self.require(requires)[0].run_script(script_name, ns)
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/site-packages/pkg_resources/__init__.py", line 1463, in run_script
    exec(code, namespace, namespace)
  File "/shares/mgehan_share/hsheng/miniconda3/envs/plantcv/lib/python3.7/site-packages/plantcv-3.11.0+3.gd86fe6b.dirty-py3.7.egg/EGG-INFO/scripts/plantcv-workflow.py", line 219, in <module>
    main()
  File "/shares/mgehan_share/hsheng/miniconda3/envs/plantcv/lib/python3.7/site-packages/plantcv-3.11.0+3.gd86fe6b.dirty-py3.7.egg/EGG-INFO/scripts/plantcv-workflow.py", line 206, in main
    plantcv.parallel.process_results(job_dir=config.tmp_dir, json_file=config.json)
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/site-packages/plantcv-3.11.0+3.gd86fe6b.dirty-py3.7.egg/plantcv/parallel/process_results.py", line 39, in process_results
    obs = json.load(results)
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/json/__init__.py", line 296, in load
    parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/json/__init__.py", line 348, in loads
    return _default_decoder.decode(s)
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/home/hsheng/miniconda3/envs/plantcv/lib/python3.7/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 29529 (char 29528)

If I delete the added code, the result can be generated properly.

[DannieSheng]

It turned out that the data type of the added observation is not compatible with JSON, so that plantcv.parallel.process_results didn't work. A pull request will be created later to check datatype when adding observation to avoid adding incompatible data.

[DannieSheng]

Addressed in #705