Return empty Much() when encountering an unknown class #5456

Job	Run time
Prepare	58s
Shellcheck	4s
Dependency	3s
Ruff check and force	15s
Check commit	38s
Create pytest cache for Python 3.13.0	16s
Create pytest cache for Python 3.12	10s
Run pytest using Python 3.13.0	20s
Run pytest using Python 3.12	15s
Process test coverage	18s
Run mypy	24s
Process test complexity	13s
Build and publish Python 🐍 distributions 📦 to TestPyPI	27s
	4m 21s

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