checker: allow `none` to be passed to `?T` #110

Job	Run time
v-up-works-nix (ubuntu-22.04, v_linux.zip)	1m 8s
v-up-works-nix (macos-13, v_macos_x86_64.zip)	3m 2s
v-up-works-nix (macos-14, v_macos_arm64.zip)	1m 15s
	5m 25s

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