[Bug] Yarn prints undefined fields w/ init

[arcanis]

Describe the bug

Running yarn init causes Yarn to print a bunch of undefined fields (instead of only the relevant ones). Additionally, the output isn't colored despite using util.inspect.

To Reproduce

1. Clone the repository
2. Run yarn build:cli
3. Run cd $(mktemp -d)
4. Run node ~/path/to/berry/packages/yarnpkg-cli/bundles/yarn.js init

Screenshots

Additional context

• There are various ways to fix this issue, but the main way I see would be to delete the empty fields in Manifest#export instead of setting them to undefined. It's usually not a problem because JSON.stringify just ignores undefined, but util.inspect doesn't.

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