feat: add getStatusPurpose method

[paullatzelsperger]

What this PR changes/adds

This PR adds a method getStatusPurpose to the RevocationListService that returns either the active status ("suspension", "revocation") or null if no status is active.

Why it does that

In IdentityHub we need to update the internal status of a VerifiableCredentialResource depending on this status.

Further notes

Linked Issue(s)

• added Result#successNullable(@Nullable T content), because results can be successful and still carry no data.
• removed the @NotNull annotation from Result#success(T content).

Relates eclipse-edc/IdentityHub#340

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.47619% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 75.02%. Comparing base (7f20ba5) to head (37cf986).
Report is 252 commits behind head on main.

Files	Patch %	Lines
...lecredentials/StatusList2021RevocationService.java	90.47%	1 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4172      +/-   ##
==========================================
+ Coverage   71.74%   75.02%   +3.28%     
==========================================
  Files         919     1007      +88     
  Lines       18457    20471    +2014     
  Branches     1037     1153     +116     
==========================================
+ Hits        13242    15359    +2117     
+ Misses       4756     4610     -146     
- Partials      459      502      +43     

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[ndr-brt]

this guard is not necessary, when the status is empty the method will return a success(null) anyway

[paullatzelsperger]

it's either the guard here, or I refactor / add a similar check in Line 76 to avoid a NPE:

 var list = res.get(true).stream()
                .filter(r -> r.getContent() != null)
                .map(AbstractResult::getContent).toList();

[ndr-brt]

nope, because the stream will be empty so the filter function will never be evaluated

[paullatzelsperger]

yes, but the .get(true) will, which is what'll cause the NPE. res is a Map<Boolean, List<Result<...>> due to the grouping

[ndr-brt]

ouch!

[ndr-brt]

in any case, you don't need to get the true, but you can stream directly on the whole credential.getCredentialStatus, because at that point there won't be any failed results.

I'm ok also with the guard anyway