[ggmarshall]

• I have reviewed all the code in this pull request and deem it of the standard expected for this project.

Since #48, Props.add_to reads props_b with .get(), so an explicit null looks the same as a missing key and the old value is kept. Before #48 (dbetto ≤ 1.3.4), a null in the overlay replaced the value.

LEGEND's dataprod configs rely on this: category overlays set tier_evt: inputs: muon_config: null to switch off the muon evt step for cal/fft/pzc/bkg/hvs. With dbetto ≥ 1.3.5 those runs silently get the muon evt step again.

This PR restores the old rule: only a key absent from props_b keeps the props_a value. It adds test_props_add_to_null_overrides, which fails on main.

Validation. pytest (31 passed), pre-commit run -a and nox -s pylint (10.00/10) all pass. I also resolved TextDB.on() for all 3,643 (validity timestamp × category) lookups in the LEGEND dataprod/config, dataprod/overrides/*, datasets/statuses and hardware/configuration/channelmaps DBs. With this branch dataprod/config is identical to dbetto 1.2.4, and against 1.4.0 the only change is the muon_config key above. Channel maps and statuses are unchanged.

Related: legend-exp/legend-dataflow#173 (callers discarding the new add_to return value).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.46%. Comparing base (5b17622) to head (45ad70a).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #62      +/-   ##
==========================================
+ Coverage   91.72%   92.46%   +0.73%     
==========================================
  Files           6        6              
  Lines         568      597      +29     
==========================================
+ Hits          521      552      +31     
+ Misses         47       45       -2     

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