fix(protocol): prevent NullPointerException in BpmnElementType

[megglos]

Description

As the elementTypeName field can be null use Optional.ofNullable in the getter.

Related issues

closes #8141

Definition of Done

Not all items need to be done depending on the issue and the pull request.

Code changes:

• The changes are backwards compatibility with previous versions
• If it fixes a bug then PRs are created to backport the fix to the last two minor versions. You can trigger a backport by assigning labels (e.g. backport stable/0.25) to the PR, in case that fails you need to create backports manually.

Testing:

• There are unit/integration tests that verify all acceptance criterias of the issue
• New tests are written to ensure backwards compatibility with further versions
• The behavior is tested manually
• The change has been verified by a QA run
• The impact of the changes is verified by a benchmark

Documentation:

• The documentation is updated (e.g. BPMN reference, configuration, examples, get-started guides, etc.)
• New content is added to the release announcement

[korthout]

Thanks for the fix @megglos 💐
This change makes perfect sense 🎉

🙃 nothing blocking, but please consider the following before merging (you can simply inform bors when you're ready):

• your commit message title doesn't comply with our commit message guidelines, specifically bpmn elements should probably be protocol.
• perhaps the pull request title could have a more meaningful name

[megglos]

@korthout thanks for the feedback, I adjusted the commit message as well as the title, is the latter now more clear?

[korthout]

@megglos thanks! 👍 (we try to make the PR titles more human readable and avoid the commit type prefix, but at the same time we are not consistent with this ourselves, so don't worry about it 😆)

[korthout]

bors merge

[ghost]

Build succeeded:

• continuous-integration/jenkins/branch

[github-actions]

Successfully created backport PR #8146 for stable/1.1.

[github-actions]

Successfully created backport PR #8147 for stable/1.2.