ValueError in apstools.plans.TuneAxis.tune._scan

[prjemian]

During USAXS testing, an error (APS-USAXS/usaxs-bluesky-ended-2023#203) was reported with this exception: ValueError: None not a valid type (int, float, ndarray, str, list, tuple). The code failed here:

/share1/bluesky/conda_envs/bluesky/lib/python3.7/site-packages/apstools/plans.py in _scan(md)
    623             if results.tune_ok.value:
    624                 yield from bps.create(name=stream_name)
--> 625                 yield from bps.read(results)
    626                 yield from bps.save()
    627

which is this code:

apstools/apstools/plans.py

Lines 623 to 626 in c6047ff

	if results.tune_ok.value:
	yield from bps.create(name=stream_name)
	yield from bps.read(results)
	yield from bps.save()

[prjemian]

Here is a ZIP file (91d5edf4.zip) with the JSON documents from the failed tune. Note that the scan completed with success but some Signal in results returned a None. The name of that Signal was not reported.

[prjemian]

Too bad that results.report() appears after the point of failure.

apstools/apstools/plans.py

Lines 623 to 632 in c6047ff

	if results.tune_ok.value:
	yield from bps.create(name=stream_name)
	yield from bps.read(results)
	yield from bps.save()
	yield from bps.mv(self.axis, final_position)
	self.stats.append(self.peaks)
	yield from bps.close_run()
	results.report()

We lack a decent diagnostic as to what went wrong.

[prjemian]

The run ended with a stop.exit_status = fail due to the ValueError. There was no PeakStats stream in the run.

[prjemian]

Need to resolve by changing two things:

1. report the results before bps.create(name=stream_name)
2. wrap the create .. read .. save with try .. except .. finally, printing a console comment if that fails

[prjemian]

Also, there is no obvious benefit from developing a unit test for this specific issue, other than the intrinsic benefit of unit tests in general.