Fix PHP 8.1 compatibility issue in ForeignNotifications
Fix PHP 8.1 compatibility issue in ForeignNotifications

Passing null to functions that expect a string is no longer allowed.
Here in this code it can apparently only happen in test scenarios.
That's why I use a very minimal workround that still calls the same
code. The lookup will return an empty string and trigger the expected
code path below.

Bug: T311448
Change-Id: If04924a22b82ae29b8f9327668e8965d6d2a490d

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo