fix(apps): Fix type information of app manager

[nickvergessen]

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[provokateurin]

Please add the return types to the method head (both interface and implementation).

[nickvergessen]

Please add the return types to the method head (both interface and implementation).

Breaks public API, so not for now

[ChristophWurst]

Looks good. Context? Is this a regression?

[provokateurin]

Breaks public API, so not for now

Why would it break something? If the data returned matches the type then it just adds additional information?

[nickvergessen]

Context? Is this a regression?

I noticed the null at some point when stepping with the debugger through the code while looking into migration service.
Did not check for the history or context

Why would it break something?

Apps implementing the interface break.
We can have a look in a follow up but I would not backport that compared to this doc block change

[nickvergessen]

/backport to stable28