Storybook 6.0 has type errors in a strict Angular 10.0.6 project

[aloifolia]

Describe the bug
With Angular strict mode enabled, the generated Storybook 6.0 code shows multiple type errors.

To Reproduce
Steps to reproduce the behavior:

1. Create a new Angular project with npx -p @angular/cli ng new storybook-test --strict
2. In the new folder, install storybook with npx sb init
3. See 4 error messages:

ERROR in /path/to/project/storybook-test/storybook-test/src/stories/button.component.ts
ERROR in /path/to/project/storybook-test/storybook-test/src/stories/button.component.ts(20,3):
TS2564: Property 'primary' has no initializer and is not definitely assigned in the constructor.

ERROR in /path/to/project/storybook-test/src/stories/button.component.ts
ERROR in /path/to/project/storybook-test/storybook-test/src/stories/button.component.ts(26,3):
TS2564: Property 'backgroundColor' has no initializer and is not definitely assigned in the constructor.

ERROR in /path/to/project/storybook-test/src/stories/button.component.ts
ERROR in /path/to/project/storybook-test/src/stories/button.component.ts(40,3):
TS2564: Property 'label' has no initializer and is not definitely assigned in the constructor.

ERROR in /path/to/project/storybook-test/src/stories/Header.stories.ts
ERROR in /path/to/project/storybook-test/src/stories/Header.stories.ts(27,3):
TS2322: Type '{}' is not assignable to type 'null | undefined'.
  Type '{}' is not assignable to type 'null'.

Expected behavior
The default installation should not show Typescript errors.

System:

Environment Info:

I am using Angular 10.0.6.

  System:
    OS: macOS Mojave 10.14.6
    CPU: (8) x64 Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
  Binaries:
    Node: 13.12.0 - ~/.nvm/versions/node/v13.12.0/bin/node
    Yarn: 1.22.4 - /usr/local/bin/yarn
    npm: 6.14.4 - ~/.nvm/versions/node/v13.12.0/bin/npm
  Browsers:
    Chrome: 84.0.4147.125
    Firefox: 77.0.1
    Safari: 13.1
  npmPackages:
    @storybook/addon-actions: ^6.0.5 => 6.0.5 
    @storybook/addon-essentials: ^6.0.5 => 6.0.5 
    @storybook/addon-links: ^6.0.5 => 6.0.5 
    @storybook/angular: ^6.0.5 => 6.0.5 

[shilman]

cc @tooppaaa @gaetanmaisse

[shilman]

Yowza!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.0.12 containing PR #12081 that references this issue. Upgrade today to try it out!

Closing this issue. Please re-open if you think there's still more to do.