fix undefined portal

[amitcnvrg]

make sure portal and ref exists before return

[codecov]

Codecov Report

Merging #334 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #334   +/-   ##
=======================================
  Coverage   97.68%   97.68%           
=======================================
  Files          27       27           
  Lines        1037     1037           
  Branches      104      104           
=======================================
  Hits         1013     1013           
  Misses          9        9           
  Partials       15       15

Impacted Files	Coverage Δ
src/mixins/treeselectMixin.js	100% <100%> (ø)	⬆️

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[P1robot]

Automated benchmark results (pass #0): passed

concurrency: 32
requests per second: 6160
concurrency: 128
requests per second: 7641
concurrency: 512
requests per second: 4685
concurrency: 1024
requests per second: 4006

[arkhamvm]

@riophae Hi. Can you accept this PR please?

[loeffel-io]

LETS GO! bug still exists since one year .. is the project dead?

[arkhamvm]

@riophae Please take a look at this PR 🙏

[abstrekt]

@riophae please accept the PR!

[micdobro]

@riophae Can you please accept the PR - this fix actually makes the project usable also in another setting.