Thanks @eddy-geek! The fix looks good, the only additional pieces we need are:

• a test locking down the correct behavior - could just be an addition to rdps011 storing an empty string, or a new test of perhaps persistence of a dropdown with various falsy values.
• a CHANGELOG entry.

💔 Note on testing dash

I have run the tests locally and they passed. (refer to testing section in contributing)

the testing section does not have any commands. I tried this .circleci snippet:

pytest --headless --nopercyfinalize --junitxml=test-reports/junit_intg.xml

but it fails with ModuleNotFoundError: No module named 'dash_renderer_test_components' apparently imported from renderer/test_multi_output.py.
so back to circleci, I adapted (needs review!) to:

git clone --depth 1 https://github.com/plotly/dash-renderer-test-components
cd dash-renderer-test-components && npm ci && npm run build:all && python setup.py sdist && pip install -e . && cd ..

next! chromedriver missing, I had to wget https://chromedriver.storage.googleapis.com/80.0.3987.106/chromedriver_linux64.zip ; unzip chromedriver_linux64.zip ;mv chromedriver ~/.local/bin

And finally it worked (with some usual chromedriver instability)

Is that the proper way or did I miss something? Shouldn't this be in the contributing guide?

@alexcjohnson ready for review. I have checked that the changed test now fails as expected without the fix, with:

$ git checkout HEAD^ dash-renderer/src/persistence.js
$ cd dash-renderer ; npm run build ; pip install -e . ; cd ..
$ pytest --headless  tests/integration/renderer/test_persistence.py::test_rdps010_toggle_persistence
>       dash_duo.wait_for_text_to_equal('#out', '')
E       selenium.common.exceptions.TimeoutException: Message: text ->  not found within 10s