LCP/ATF data is malformed when no LCP is found by the beacon about wp-rocket HOT 2 OPEN

Bringing back to ToDo as this is not fixed: I still have errors when re-visiting the page and the LCP value in case of not found is not "not found" but null.
There are several issues:

1. the beacon script sends an "image" with lcp label, even if there is no element.
   To fix this, I modified "topCandidates" in the beacon by adding a filter to take out items where the getElementInfo did not find anything relevant:

	const topCandidates = potentialCandidates.map(element => {
		const rect = element.getBoundingClientRect();
		return {
			element: element,
			rect: rect,
		};
	}).filter(item => {
		return (
			item.rect.width > 0 &&
			item.rect.height > 0 &&
			isIntersecting(item.rect)
		);
	})
	.map(item => ({
		item,
		area: getArea(item.rect),
		elementInfo: getElementInfo(item.element),
	}))
	.filter(item => {
		return (
			item.elementInfo !== null && 
			item.elementInfo.type !== ""
		);
	})
	.sort((a, b) => b.area - a.area)
	.slice(0, count);

The issue is that, even if getElementInfo does not find anything, it returns an elementInfo with a dummy structure. Hence, the check later on const firstElementWithInfo = above_the_fold_images.find(item => item.elementInfo !== null); seems useless! There will always be a elementInfo ; but a dummy one sometimes.
It might not be the right way to do it, but the 1st issue is here: notice that without this fix, we don't have the log "No LCP element found" on http://mathieu.e2e.rocketlabsqa.ovh/ for instance. This shows that the beacon thinks there is an LCP becasue it does not filter out empty/irrelevant elements.

2. Once this is fixed, instead of null in the DB, I get "not found". Be careful, the " are actually in the string! This leads to the following warning logs:

[25-Apr-2024 16:53:58 UTC] PHP Warning:  Attempt to read property "type" on string in /var/www/html/mathieu.e2e.rocketlabsqa.ovh/wp-content/plugins/wp-rocket/inc/Engine/Media/AboveTheFold/Frontend/Controller.php on line 250
[25-Apr-2024 16:53:58 UTC] PHP Warning:  Attempt to read property "type" on string in /var/www/html/mathieu.e2e.rocketlabsqa.ovh/wp-content/plugins/wp-rocket/inc/Engine/Media/AboveTheFold/Frontend/Controller.php on line 143

The issue is: the check in has_lcp $lcp !== 'not found' is true because '"not found"' !== 'not found'
I think the additional " comes from the use of wp_json_encode in 'lcp' => wp_json_encode( $lcp ),
two choices here: either change how we write into the DB in case $lcp = 'not found' to avoid adding the additional ", or change the has_lcp check.

After this, it seems working as expected, without logs.

One should check this, fix and ensure the modifications don't break tests on Rocket-E2E.

from wp-rocket.

Note: other page template without images on e2e https://e2e.rocketlabsqa.ovh/lcp_no_images/

from wp-rocket.