Fix error thrown when the task_class of a task is None

[backmari]

Short description of the changes:

Tasks added using the Django admin interface will have task_class equal to None if it is left empty. A task with task_class equal to None caused an error to be thrown in workflow_app in the WebMon test environment. This PR adds a check for None before the call to strip() and a unit test.

INFO:2024-02-27 14:52:37,039 arcs r201562: POSTPROCESS.DATA_READY: {'facility': 'SNS', 'instrument': 'arcs', 'ipts': 'IPTS-27800', 'run_number': 201562, 'data_file': '/SNS/ARCS/IPTS-27800/nexus/ARCS_201562.nxs.h5', 'information': 'Requested by u5z'}
ERROR:2024-02-27 14:52:37,061 Listener failed to process message:
Traceback (most recent call last):
  File "/opt/conda/lib/python3.10/site-packages/workflow/amq_listener.py", line 61, in on_message
    action(headers, message)
  File "/opt/conda/lib/python3.10/site-packages/workflow/state_utilities.py", line 70, in process_function
    return action(self, headers, message)
  File "/opt/conda/lib/python3.10/site-packages/workflow/states.py", line 84, in __call__
    self._call_db_task(task_data, headers, message)
  File "/opt/conda/lib/python3.10/site-packages/workflow/states.py", line 56, in _call_db_task
    if "task_class" in task_def and len(task_def["task_class"].strip()) > 0:
AttributeError: 'NoneType' object has no attribute 'strip'

Check list for the pull request

• I have read the [CONTRIBUTING]
• I have read the [CODE_OF_CONDUCT]
• I have added tests for my changes
• I have updated the documentation accordingly

Check list for the reviewer

• I have read the [CONTRIBUTING]
• I have verified the proposed changes
• best software practices
  • all internal functions have an underbar, as is python standard
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

Manual test for the reviewer

References

Story 2822: Test post processing agent v3.0 in test environment

[peterfpeterson]

I like the new tests