[Bug]: SB v8 beta empty source code (disable on purpose) in not working as in v7

Describe the bug

In v7 we could override the source parameter to disable code in Doc pages.

Example is also here.

In the latest v8 beta 8.0.0-beta.5, the source code of null results in a clickable Show Code button that displays effectively nothing.

https://github.com/storybookjs/storybook/assets/12672541/b3384464-e057-4c92-9f7e-0c2d421844ec

To Reproduce

A reproduction repo is here generated by npx storybook@next sandbox: https://github.com/konsalex/sb-null-source-code/blob/main/src/stories/Button.stories.ts#L12

System

Storybook Environment Info:

  System:
    OS: macOS 14.3.1
    CPU: (10) x64 Apple M1 Max
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.7.0 - ~/Library/Caches/fnm_multishells/9693_1708939965986/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn <----- active
    npm: 10.1.0 - ~/Library/Caches/fnm_multishells/9693_1708939965986/bin/npm
    pnpm: 8.6.0 - ~/Library/pnpm/pnpm
  Browsers:
    Chrome: 121.0.6167.184
    Safari: 17.3.1
  npmPackages:
    @storybook/addon-essentials: ^8.0.0-beta.5 => 8.0.0-beta.5
    @storybook/addon-interactions: ^8.0.0-beta.5 => 8.0.0-beta.5
    @storybook/addon-links: ^8.0.0-beta.5 => 8.0.0-beta.5
    @storybook/addon-onboarding: ^1.0.11 => 1.0.11
    @storybook/blocks: ^8.0.0-beta.5 => 8.0.0-beta.5
    @storybook/react: ^8.0.0-beta.5 => 8.0.0-beta.5
    @storybook/react-vite: ^8.0.0-beta.5 => 8.0.0-beta.5
    @storybook/test: ^8.0.0-beta.5 => 8.0.0-beta.5
    storybook: ^8.0.0-beta.5 => 8.0.0-beta.5

Additional context

No response