fix: should still be able to jsonMerge() even if currently null

[cyjake]

att

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.79%. Comparing base (8f97cc5) to head (2111e61).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #432   +/-   ##
=======================================
  Coverage   96.79%   96.79%           
=======================================
  Files          45       45           
  Lines        3716     3716           
  Branches       72       72           
=======================================
  Hits         3597     3597           
  Misses        105      105           
  Partials       14       14           

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