Storybook controls shouldn't pass 'undefined' by default

Now that storybook doesn’t infer defaults for controls since 6.3+, there’s an unexpected behavior where stories will get undefined explicitly as control values. This can mess up some components (in this case, React), because { someProp: undefined } is different than {} and it will result in strange behavior. For example, if you’re handling defaults by doing something like { ...DEFAULT_PROPS, props }, then a value of undefined will overwrite the default.

See discussion in issue #15378 for more details. Seems like this was introduced in #14579.

Mentioning people involved / with the same issue: tmeasday shilman penx mboettcher

[shilman]

Crikey!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.3.5 containing PR #15654 that references this issue. Upgrade today to the @latest NPM tag to try it out!

npx sb upgrade

[tmeasday]

@pupudu I suppose the disabled case isn’t all that different as from the core’s perspective there should be no difference (disabling it just means show no UI to change/set it).