fix(bundle): don't look for a $ref pointer on a null value

[erunion]

We had some customers of our CLI tool report issues¹ this morning of sudden crashes when attempting to validate an OpenAPI definition after we published a new release of our OpenAPI parser¹ that included an upgrade from v13.0.5 to v14.1.0 with the following error:

Cannot read properties of null (reading '$ref')

We were able to narrow it down to a regression introduced in #391 where it looks for a $ref pointer to supply to the onBundle callback. The problem our customers had, and we were able to reproduce, encountered with this was on nullish schema examples and this work attempting to look for a $ref pointer in it:

The fix I've submitted here is to just wrap this check in a type assertion to ensure that we're only looking for a $ref pointer in an object.

Footnotes

1. https://github.com/readmeio/rdme/issues/1306 ↩ ↩²

[jonluca]

LGTM - thanks!

[coveralls]

Pull Request Test Coverage Report for Build 16305772887

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.4%) to 88.679%

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Totals
Change from base Build 16106900928:	0.4%
Covered Lines:	1767
Relevant Lines:	1952

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💛 - Coveralls

[github-actions]

🎉 This PR is included in version 14.1.1 🎉

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