Allow `None` in rehydration #564

Job	Run time
sdist	8s
changes	4s
macos (x86_64)	40s
macos (aarch64)	40s
linux (x86_64)	52s
windows (x64)	1m 4s
linux (x86)	1m 0s
windows (x86)	2m 20s
linux (aarch64)	1m 17s
linux (armv7)	1m 25s
linux (s390x)	1m 14s
linux (ppc64le)	1m 15s
Build and push base postgres image	0s
Build and push base pyrust	0s
test	0s
	11m 59s

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