fix: define popupVisible to undefined, trigger will be failed.

[shiasn]

当 popupVisible 定义为 undefined 时，popup 将无法触发

[codecov]

Codecov Report

Merging #221 (435c102) into master (960f146) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #221   +/-   ##
=======================================
  Coverage   88.95%   88.95%           
=======================================
  Files          11       11           
  Lines         516      516           
  Branches      130      130           
=======================================
  Hits          459      459           
  Misses         57       57           

Impacted Files	Coverage Δ
src/index.tsx	85.02% <100.00%> (ø)

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