Fix openAsync example tristate pattern

[KIMGEONHWI]

This PR fixes the openAsync example to properly demonstrate the tristate pattern (true/false/undefined) for better understanding of the API usage.

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Latest commit: 5fbeb7a

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.85%. Comparing base (6a96688) to head (5fbeb7a).

Additional details and impacted files

@@ Coverage Diff @@ ## main #210 +/- ## ======================================= Coverage 99.85% 99.85% ======================================= Files 15 15 Lines 1340 1340 Branches 262 262 ======================================= Hits 1338 1338 Misses 2 2 

Components	Coverage Δ
overlay-kit	99.85% <0.00%> (ø)

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