[Validator] fixed the wrong isAbstract() check against the class (fixed #8589)
merged branch marcj/ticket_8589 (PR #8728)

This PR was merged into the 2.2 branch.

Discussion
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[Validator] Fixed the wrong isAbstract() call in PR #8592

| Q             | A
| ------------- | ---
| Bug fix?      | [yes]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | [#8589]
| License       | MIT
| Doc PR        | [n/a]

Commits
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18896d5a [Validator] fixed the wrong isAbstract() check against the class (fixed #8589)