[JENKINS-76360] Fix NPE on TAP Test Results screen

[janfaracik]

Would appreciate some insight from plugin maintainers here. I've fixed the null pointer issue, essentially caused by expected methods not existing in this plugin setup. The getTarget call made this a little more complicated to debug initially, so would appreciate a review.

Testing done

• Screen appears, title shows, tests show

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[kinow]

The code changes look OK @janfaracik , but I'm not following the API changes in Jenkins (haven't done so in years). I'll need some time to review their API and see if I can confirm if there's anything dangerous here, something that needs a test, etc. Thanks for the PR!