Fix NPEs after OnSharedPreferenceChangeListener changes

[Stypox]

What is it?

• Bugfix (user facing)
• Feature (user facing)
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

According to OnSharedPreferenceChangeListener's documentation, this was caused by #9306 (even though it is not mentioned in Android 11's upgrading page):

Apps targeting API 30 on devices running OS versions Android R/11 or later, will receive a null value when preferences are cleared.

So I modified all of our overrides of that function to make sure to handle null values gracefully.

Fixes the following issue(s)

• Fixes [Nightly] Crash on Importing Database #9692

APK testing

The APK can be found by going to the "Checks" tab below the title. On the left pane, click on "CI", scroll down to "artifacts" and click "app" to download the zip file which contains the debug APK of this PR.

Due diligence

• I read the contribution guidelines.

[TobiGr]

don't merge yet

[Stypox]

Mmmh, strange, I asked AS to give me a list of all implementors... Apparently I missed something, thanks for double-checking. :-)

[TobiGr]

i used grep, i don't trust AS anymore xD

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
5 Code Smells

0.0% Coverage
0.0% Duplication

[Stypox]

Noteworthy code smell from sonar and Android Studio about this:

Notifications should only launch a Service from notification actions (addAction)

But I just tested in API 33 and there was no issue tapping on the notification

[TobiGr]

Those should be addressed in a separate PR. I only fixed Sonar here because it blocked merging this PR.