fix: obfuscation of an array element can lead to undefined error

[phanshiyu]

why

In normal circumstances, we should expect that there will be no leaf node in a document that will be undefined, since in JSON land, which is the type that we will always serialise, does not have such a primitive. This is the reason why we only handle known JSON primitive types in traverseAndFlatten, and throw otherwise.

The problem comes during obfuscation, when traverseAndFlatten is used to flatten leaf nodes that are to be removed. We do so by using lodash's pick on our document, that in cases where there are arrays involved, array items that are not picked, will be left as an undefined/<empty item>.

pick([1,2,3,4], 3) will result in [undefined, undefined, undefined, 4] which is passed to traverseAndFlatten which then throws because now it encounters an unexpected type.

what

1. Added a flag on traverseAndFlatten to remove undefined values instead of throwing, it defaults to false
2. Switch flag to true in obfuscation

[github-actions]

🎉 This PR is included in version 6.10.0-beta.7 🎉

The release is available on:

• npm package (@beta dist-tag)
• GitHub release

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