Fix DeploymentConfig::getAllEnvOverrides memoization when no MAGENTO_…

[hryvinskyi]

Description (*)

DeploymentConfig::getAllEnvOverrides() has a broken memoization pattern that causes significant performance degradation on every request.

The method uses empty($this->envOverrides) to determine whether the environment variable scan has already been performed. However, when no MAGENTO_DC_* environment variables exist (which is the common case for most Magento installations), $this->envOverrides remains as [], and empty([]) evaluates to true — causing the full getenv() loop to execute on every single call.

The fix changes the initialization of $envOverrides from [] to null and uses a strict === null check as the guard condition. This ensures the getenv() scan runs exactly once per request lifecycle, regardless of whether any MAGENTO_DC_* variables are found.

Manual testing scenarios (*)

1. Deploy a Magento instance without any MAGENTO_DC_* environment variables set (default setup).
2. Profile a frontend page request using SPX, Blackfire, or Xdebug.
3. Search for getAllEnvOverrides in the profile — before the fix it will show a lot of calls
4. Apply the patch and profile the same page again.
5. Confirm getAllEnvOverrides now shows ~1-2 calls with negligible time.
6. Set a MAGENTO_DC_* environment variable (e.g., MAGENTO_DC_DB__CONNECTION__DEFAULT__HOST=127.0.0.1).
7. Verify the env override is correctly applied to DeploymentConfig::get('db/connection/default/host').
8. Verify resetData() still works correctly (e.g., after bin/magento app:config:import).

Questions or comments

This is a one-line logic fix with meaningful performance impact. The root cause is that empty() cannot distinguish between "never scanned" and "scanned but found nothing." Using null as the uninitialized sentinel resolves this cleanly.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email psirt@adobe.com.

[hryvinskyi]

@magento run all tests