fix: create ErrorState with error.message is undefined

[cehan-Chloe]

Falls back to error.toString() if message is undefined/null, and uses "Unknown error" if no error object exists at all.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (10d3f91) to head (9d2f374).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #845   +/-   ##
===========================
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