Allow author field to be "" (string of length 0)

[joulev]

I was play around with the comment pages and attempted to post some comments. However, anonymous comments cannot be submitted.

POST /api/comments

{
  "author": "",
  "text": "hello, world",
  "pageId": "anything"
}

fails because author doesn't pass the check

ezkomment/server/middlewares/sanitizeRequests/comments.ts

Lines 17 to 25 in dd993cd

	if (
	author !== undefined &&
	author !== null &&
	(typeof author !== "string" || !COMMENT.authorIsValid(author))
	) {
	throw new CustomApiError(
	"'author' must be a non-empty string, undefined or null. If undefined, 'author' will be casted to null."
	);
	}

In fact since the field is taken from an HTML input field, author is always a string – if the user doesn't fill in then it's "" like above.

This means the validation is buggy. This PR tries to fix it.

[joulev]

This blew my mind and I feel utterly embarrassed for not knowing it in advance.

---

This can be seen as a special case of the logical OR (||) operator, which returns the right-hand side operand if the left operand is any falsy value, not only null or undefined. In other words, if you use || to provide some default value to another variable foo, you may encounter unexpected behaviors if you consider some falsy values as usable (e.g., '' or 0). See below for more examples.

[codecov]

Codecov Report

Merging #213 (94ab266) into main (dd993cd) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 94ab266 differs from pull request most recent head ffd6727. Consider uploading reports for the commit ffd6727 to get more accurate results

@@            Coverage Diff             @@
##             main     #213      +/-   ##
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- Coverage   96.49%   96.49%   -0.01%     
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  Files          38       38              
  Lines         856      855       -1     
  Branches      174      174              
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- Hits          826      825       -1     
  Misses         27       27              
  Partials        3        3              

Impacted Files	Coverage Δ
misc/validate.ts	100.00% <ø> (ø)