[cache] fix a cache issue with an entity created without relation cache prefill Prefilling the relation cache has its benefits sometimes, but for massive imports it may be a memory hog. The caches should be kept coherent even if there was no prefill. Closes #3828155.

.. _cwprops:

The property mecanism
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.. XXX CWProperty and co


Property API
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.. XXX feed me

Registering and using your own property
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.. XXX feed me