Fix std::nullptr_t deduction issues. #279

Job	Run time
build (ubuntu-latest, Debug, clang)	45s
build (ubuntu-latest, Debug, gcc)	29s
build (ubuntu-latest, Debug, tcc)	32s
build (ubuntu-latest, RelWithDebInfo, clang)	48s
build (ubuntu-latest, RelWithDebInfo, gcc)	49s
build (ubuntu-latest, RelWithDebInfo, tcc)	25s
build (ubuntu-latest, MinSizeRel, clang)	46s
build (ubuntu-latest, MinSizeRel, gcc)	36s
build (ubuntu-latest, MinSizeRel, tcc)	24s
build (ubuntu-latest, Release, clang)	58s
build (ubuntu-latest, Release, gcc)	53s
build (ubuntu-latest, Release, tcc)	40s
build (windows-latest, Debug, default)	1m 13s
build (windows-latest, Debug, clang)	2m 18s
build (windows-latest, Debug, gcc)	2m 26s
build (windows-latest, RelWithDebInfo, default)	1m 0s
build (windows-latest, RelWithDebInfo, clang)	1m 33s
build (windows-latest, RelWithDebInfo, gcc)	2m 38s
build (windows-latest, MinSizeRel, default)	53s
build (windows-latest, MinSizeRel, clang)	1m 2s
build (windows-latest, MinSizeRel, gcc)	3m 9s
build (windows-latest, Release, default)	1m 4s
build (windows-latest, Release, clang)	2m 3s
build (windows-latest, Release, gcc)	2m 9s
build (macos-11, Debug, default)	30s
build (macos-11, RelWithDebInfo, default)	39s
build (macos-11, MinSizeRel, default)	37s
build (macos-11, Release, default)	39s
build (macos-14, Debug, default)	12s
build (macos-14, RelWithDebInfo, default)	15s
build (macos-14, MinSizeRel, default)	16s
build (macos-14, Release, default)	13s
	32m 54s

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