Fix PHP Warning when accessing user_login property on boolean

[devin-ai-integration]

Fix PHP Warning when accessing user_login property on boolean

Issue

Fixes #24

This PR addresses a PHP Warning that occurs when attempting to read the property "user_login" on a boolean value within the Shifter WordPress MU plugin.

Root Cause

The notify_logout method in class-shifter-api.php doesn't validate the result of get_user_by('ID', $user_id) before attempting to access the user_login property. When an invalid user ID is passed, get_user_by() returns false, causing a PHP warning.

Solution

Added validation to check if $user is a valid user object before accessing its properties. The method now gracefully handles cases where get_user_by() returns false without throwing PHP warnings.

Testing

The fix has been tested by verifying that:

• The code properly handles cases where get_user_by() returns false
• No PHP warnings are generated when an invalid user ID is passed to the notify_logout method

Link to Devin run

https://app.devin.ai/sessions/c8ccda563c184048acd7683871e96dab

Requested by: hidetaka@digitalcube.jp

[devin-ai-integration]

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