Prevent traversing over a null value

[diedexx]

Context

If an option group is requested that doesn't exist or the option_instance isn't registered yet, you'll get a warning: PHP Warning: foreach() argument must be of type array|object, null given in [..]/wordpress-seo/inc/options/class-wpseo-options.php on line 583.

This shows up in the logs after Yoast is activated but before the customer ever logs into wp-admin.

Summary

This PR can be summarized in the following changelog entry:

• Fixes a PHP warning when when requesting an option that doesn't exist or isn't registered yet.

Relevant technical choices:

• This change aims to solve this in a BC manner; No behavior is changed.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #

[coveralls]

Pull Request Test Coverage Report for Build 2b48c1aa7c288f80f53f34c9e5612e61b4700957

Details

• 1 of 2 (50.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 52.867%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
inc/options/class-wpseo-options.php	1	2	50.0%

Totals
Change from base Build c3330232123cc641935e63cd29eb906a15222c04:	-0.5%
Covered Lines:	31460
Relevant Lines:	59652

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💛 - Coveralls