Add missing value sentinel

[rbeucher]

Set Sentinel FILLVALUE for variable mrsofc static file

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.7%. Comparing base (a8d360d) to head (87fc09f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #496   +/-   ##
=====================================
  Coverage   78.7%   78.7%           
=====================================
  Files         33      33           
  Lines       6558    6558           
  Branches    1242    1242           
=====================================
  Hits        5163    5163           
  Misses      1127    1127           
  Partials     268     268           

Flag	Coverage Δ
unit	78.7% <ø> (ø)

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