Slideshow: do not render markup when user doesn't select any images

[cpapazoglou]

This PR resolves #15273, where adding a slideshow block, without selecting any image, results to obsolete markup in the frontend. Especially, in the case of AMP rendering there was an extra visible markup.

Changes proposed in this Pull Request:

• Return null when images array is empty so that no obsolete markup is rendered both for normal and AMP rendering

Jetpack product discussion

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Setup local jetpack env with ngrok tunneling as per instructions
• Install the AMP plugin By AMP Project Contributors here /wp-admin/plugin-install.php?s=amp&tab=search&type=term
• Go to /wp-admin/post-new.php
• Add a slideshow block AND do not select any image
• Save and visit the above post
• Visit the the same post by appending /amp to the URL to inspect how AMP renders

Before

After

Before AMP

After AMP

Proposed changelog entry for your changes:

• Slideshow: do not render markup when user doesn't select any images

Notices

The above changes will work for:

• new content both for normal and AMP rendering
• old content for AMP rendering

The above changes will not work for:

• old content for normal rendering

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello cpapazoglou! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D45278-code before merging this PR. Thank you!
This revision will be updated with each commit to this PR

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

E2E results is available here (for debugging purposes): https://jetpack-e2e-dashboard.herokuapp.com/pr-16231

Scheduled Jetpack release: July 7, 2020.
Scheduled code freeze: June 30, 2020

Generated by 🚫 dangerJS against aff2683

[frontdevde]

Thanks for swiftly addressing the feedback!

I tested as per testing instructions and can confirm that the Slideshow isn't rendered anymore when no images are selected. This is true for both the normal and AMP view.

LGTM 👍

[jeherve]

This tests well for me, it should be good to merge! 🚢

[cpapazoglou]

r209584-wpcom