saxswaxs_to_chap.py failure when not performing background subtraction

[arwoll]

Describe the bug
In back and forth with Kelly trying to use saxsaxs_to_chap.py: Tried running it with background subtraction processors taken out. This resulted in a new error:

Running from /nfs/chess/auxiliary/reduced_data/cycles/2026-1/id3b/dufresne-4795-a/analysis/woll:

~chess_id3b/aux_id3b/git_repos/saxswaxs-automation/saxswaxs_to_chap.py -m map_MR3-50to1_I50_5to15min_flymesh_001_cust.yaml -t ../manual_yaml/*.yaml
Warning: Skipping map data validation for Epoch
Warning: Skipping map data validation for start_time
Warning: Skipping map data validation for presample_intensity
Warning: Skipping map data validation for dwell_time_actual
Warning: Skipping map data validation for postsample_intensity
Warning: Skipping map data validation for Epoch
Warning: Skipping map data validation for start_time
Warning: Skipping map data validation for presample_intensity
Warning: Skipping map data validation for dwell_time_actual
Warning: Skipping map data validation for postsample_intensity
Warning: Skipping data file validation for detectors ['PIL5']
Warning: Skipping data file validation for detectors ['PIL9', 'PIL11']
Writing to /nfs/chess/auxiliary/reduced_data/cycles/2026-1/id3b/dufresne-4795-a/analysis/woll/pyfai_integration_processor_config.yaml
Traceback (most recent call last):
File "/home/chess_id3b/aux_id3b/git_repos/saxswaxs-automation/saxswaxs_to_chap.py", line 711, in
chap_config = wf_to_chap(wf, args.outputdir, map_filename=args.map_config_file)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/chess_id3b/aux_id3b/git_repos/saxswaxs-automation/saxswaxs_to_chap.py", line 189, in wf_to_chap
'convert': [
^
TypeError: Value after * must be an iterable, not NoneType

Given the context of the error in wf_to_chap:

    **update_pipelines,
    'convert': [
        {
            'common.ZarrToNexusProcessor': {
                'zarr_filename': 'data.zarr',
                'nexus_filename': 'data.nxs',
            }
        },
        *background_pipeline,
        *_correction_pipelines,
        *makelink_pipelines(wf),
        *_restructure_pipeline,
    ],

I speculate that "background_pipeline" might now be empty and is the culprit.