Return empty Much() when encountering an unknown class #5462

Job	Run time
Prepare	1m 5s
Shellcheck	3s
Dependency	6s
Ruff check and force	14s
Check commit	39s
Create pytest cache for Python 3.13.0	18s
Create pytest cache for Python 3.12	6s
Run pytest using Python 3.13.0	20s
Run pytest using Python 3.12	16s
Run mypy	23s
Process test coverage	23s
Build and publish Python 🐍 distributions 📦 to TestPyPI	29s
Process test complexity	13s
	4m 35s

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