fix(ui): handle null oldObj in deepDiff to prevent refresh failure

[JosephKav]

if (oldObj === undefined) return newObj;
const keys = Object.keys(oldObj).concat(Object.keys(newObj));

If 'oldObj' is null, it would get past the undefined check, but crash on Object.keys of null

fixes #514

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.56%. Comparing base (3cf9060) to head (41dfd61).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #515   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files         120      120           
  Lines       10279    10279           
=======================================
  Hits        10130    10130           
  Misses        121      121           
  Partials       28       28           

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