fix: Prevent null snapshots from being stored and causing errors

[chrisbreiding]

• Closes Undefined snapshot on test failure #15816

User facing changelog

• Fixed an issue where hovering over a command log without a snapshot would cause the error Cannot read property 'name' of null

Additional details

Snapshotting can fail for various reasons. In the issue this closes, it was because the snapshot happens before the page fully loads, but it can also fail if the page is cross-origin. We catch such failures when creating the snapshot and return null, but the log adds that null value to the list of snapshots. When the user hovers over the command and we try to display the snapshot, it's expected to be a proper snapshot object and throws when we try to access properties on it. The solution is simply to not add null snapshots to the list of the log's snapshots. Then it's properly recognized as "missing" (which is correct, since we can't get a snapshot of it) and we display that to the user without erroring.

How has the user experience changed?

Hovering over commands with a missing snapshot no longer errors.

PR Tasks

• Have tests been added/updated?
• Has the original issue or this PR been tagged with a release in ZenHub?
• N/A Has a PR for user-facing changes been opened in cypress-documentation?
• N/A Have API changes been updated in the type definitions?
• N/A Have new configuration options been added to the cypress.schema.json?

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[cypress]

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Test summary

9493 • 0 • 111 • 3 • 1

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Run details

Project	cypress
Status	Passed
Commit	adc1813
Started	Apr 15, 2021 4:00 PM
Ended	Apr 15, 2021 4:13 PM
Duration	12:54 💡
OS	Linux Debian - 10.8
Browser	Multiple

View run in Cypress Dashboard ➡️

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Flakiness

	cypress/integration/retries.ui.spec.js		1
1	runner/cypress retries.ui.spec > opens attempt on each attempt failure for the screenshot, and closes after test passes

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[bahmutov]

Perfect, fixes my test case repo, when hovering shows "snapshot is missing", nice

[bahmutov]

meant to approve it right away