fix: support partial document in asLink() and documentToLinkField()

[angeloashmore]

Types of changes

• Chore (a non-breaking change which is related to package maintenance)
• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

This PR fixes a bug where asLink() would throw an error when given a Prismic document without a data property.

import * as prismicH from "@prismicio/helpers";

asLink({}); // Throws

The following error is thrown (the stacktrace has been truncated):

TypeError {
  message: 'Cannot convert undefined or null to object',
}

› Function.keys (<anonymous>)
› null.documentToLinkField (node_modules/@prismicio/helpers/src/documentToLinkField.ts:39:14)
› Object.asLink (node_modules/@prismicio/helpers/src/asLink.ts:62:6)

This happens because documentToLinkField() tries to call Object.keys() on document.data, which is undefined.

Although asLink() (and its underlying documentToLinkField()) is typed to only accept full Prismic documents, a partial document could be passed in untyped projects.

Context

The issue this PR solves was discovered while resolving this @prismicio/react issue: prismicio/prismic-react#150

Checklist:

• My change requires an update to the official documentation.
• All TSDoc comments are up-to-date and new ones have been added where necessary.
• All new and existing tests are passing.

🐳

[github-actions]

size-limit report 📦

Path	Size
dist/index.js	3.1 KB (+0.13% 🔺)
dist/index.cjs	3.64 KB (+0.09% 🔺)

[lihbr]

LGTM, I'll release and let you proceed on the React side :)

[lihbr]

Released in 2.3.1: https://github.com/prismicio/prismic-helpers/blob/master/CHANGELOG.md#231-2022-06-09 🎉