Failure to Inherit Unbiased Template

[JS650]

Describe the bug
When running the preprocessing stage of the RABIES pipeline, inheriting an unbiased template (using the --inherit_unbiased_template flag) fails if the run used to generate the template did not include a mask file (i.e., --commonspace_reg masking=false,brain_extraction=false,template_registration=SyN,fast_commonspace=false).

Describe RABIES call
RABIES command:

singularity run \\
--bind $RABIES_DIR/input \\
--bind $RABIES_DIR/preproc5_1 \\
--bind $RABIES_DIR/preproc_unbiastemp_1 \\
$RABIES_DIR/rabies.sif --exclusion_ids $RABIES_DIR/preproc5_1/scans_to_exclude.txt -p MultiProc --local_threads 8 preprocess $RABIES_DIR/input $RABIES_DIR/preproc5_1 --bids_filter $RABIES_DIR/preproc5_1/BIDS_FILTER.json --commonspace_resampling 0.2x0.2x0.2 --inherit_unbiased_template $RABIES_DIR/preproc_unbiastemp_1 --bold2anat_coreg masking=true,brain_extraction=false,registration=SyN

Attach log file
rabies_preprocess.log

Attach QC_report
No QC_report is generated. Bug occurs during the setup stage of preprocessing.

Additional context
The specific error encountered is as follows (note this is not printed to the log file):

Traceback (most recent call last):
  File "/opt/conda/bin/rabies", line 7, in <module>
    exec(compile(f.read(), __file__, 'exec'))
  File "/home/mambauser/RABIES/scripts/rabies", line 3, in <module>
    execute_workflow()
  File "/home/mambauser/RABIES/rabies/run_main.py", line 51, in execute_workflow
    workflow = preprocess(opts, log)
  File "/home/mambauser/RABIES/rabies/run_main.py", line 243, in preprocess
    workflow = init_main_wf(opts.bids_dir, opts.output_dir, opts)
  File "/home/mambauser/RABIES/rabies/preprocess_pkg/main_wf.py", line 235, in init_main_wf
    opts, inherit_dict = inherit_unbiased_files(opts.inherit_unbiased_template, opts)
  File "/home/mambauser/RABIES/rabies/preprocess_pkg/commonspace_reg.py", line 785, in inherit_unbiased_files
    if not os.path.isfile(inherit_dict[key]):
  File "/opt/conda/lib/python3.9/genericpath.py", line 30, in isfile
    st = os.stat(path)
TypeError: stat: path should be string, bytes, os.PathLike or integer, not _Undefined
``

The problem is that using an inherited unbiased template relies on there being an associated mask file generated. If this isn't specified (using --commonspace_reg masking=*true*...), there will be no path for the mask variable and this error will arise.