Fix std::nullptr_t deduction issues. #135

Job	Run time
build (ubuntu-latest, Debug, address)	46s
build (ubuntu-latest, Debug, memory)	27s
build (ubuntu-latest, Debug, undefined)	24s
build (ubuntu-latest, RelWithDebInfo, address)	30s
build (ubuntu-latest, RelWithDebInfo, memory)	34s
build (ubuntu-latest, RelWithDebInfo, undefined)	33s
build (ubuntu-latest, MinSizeRel, address)	26s
build (ubuntu-latest, MinSizeRel, memory)	27s
build (ubuntu-latest, MinSizeRel, undefined)	37s
build (ubuntu-latest, Release, address)	30s
build (ubuntu-latest, Release, memory)	29s
build (ubuntu-latest, Release, undefined)	38s
build (macOS-latest, Debug, address)	32s
build (macOS-latest, Debug, undefined)	49s
build (macOS-latest, RelWithDebInfo, address)	30s
build (macOS-latest, RelWithDebInfo, undefined)	55s
build (macOS-latest, MinSizeRel, address)	27s
build (macOS-latest, MinSizeRel, undefined)	1m 0s
build (macOS-latest, Release, address)	3m 12s
build (macOS-latest, Release, undefined)	1m 5s
	14m 51s

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