[Reference] fix namespace in Expression constraint
bug #4153 [Reference] fix namespace in Expression constraint (xabbuh)

This PR was merged into the 2.4 branch.

Discussion
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[Reference] fix namespace in Expression constraint

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.4+
| Fixed tickets |

Commits
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1deabde [Reference] fix namespace in Expression constraint