addon-knobs: null default prop is false after page reload

[binomialstew]

When setting a boolean default prop value, for example, const shouldBeNullByDefault = boolean('Should Be Null By Default', null);, the value is null but changes to false if page is reloaded.

Steps to reproduce

Clone repo:
git@github.com:CLL80/storybook.git

Checkout branch:
knob-test

Run storybook

Go to the withKnobs story:
http://localhost:9011/?selectedKind=Addons%7CKnobs.withKnobs&selectedStory=tweaks%20static%20values

You will see a <h3> that was added at the top of the story. "Should be `null` by default: null".

Reload the page, and null will now be false. This is important because when it is false, the prop will be passed to the component, but if it was null, it would not.

Please specify which version of Storybook and optionally any affected addons that you're running

@storybook/react 4.0.0-alpha.2
@storybook/addon-knobs 4.0.0-alpha.2

I first noticed this issue using v3.3.10.

[mshaaban088]

Just some insights about this issue, this is happening because:

• First time the value is null, serialized as 'null' (String), and stored in query-params
• When you reload the page, the value is loaded
  • First from stories (value is still null)
  • Second from the query params, which has the serialized version of type String, and when the deserialization happens (value === 'true') it ends having value equals to false

See Serialization/Deserialization

[mshaaban088]

I'm going to write a small fix for it

[Hypnosphi]

Released as 3.4.2