Make a simple of mutable json by copy

[codecov[bot]]

Codecov Report

Merging #185 (7fcaa9b) into main (cd857d0) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 7fcaa9b differs from pull request most recent head eccff02. Consider uploading reports for the commit eccff02 to get more accurate results

@@           Coverage Diff           @@
##             main     #185   +/-   ##
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  Coverage   88.82%   88.82%           
=======================================
  Files           9        9           
  Lines        1691     1691           
=======================================
  Hits         1502     1502           
  Misses        189      189           

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[quinnj]

Thanks @xiaodaigh!