Build

Replace NULL with nullptr #539

Job	Run time
windows (win64_msvc2019_64, 3.13, x64, 5.15.*, PythonQtCore PythonQtGui PythonQtMultimedia)	3m 46s
oldschool (rockylinux, 9, release)	4m 26s
windows (win32_mingw53, 3.6, x86, 5.11.*)	6m 24s
oldschool (rockylinux, 9, debug)	4m 3s
windows (win64_mingw73, 3.10, 5.12.*, x64)	5m 40s
macOS (latest, 3.11, 5.12.*, debug)	5m 58s
macOS (latest, 3.9, 5.9.*, debug)	6m 45s
ubuntu (22.04)	7m 0s
windows (win64_msvc2017_64, 3.6, x64, 5.11.*)	4m 30s
ubuntu (24.04)	6m 49s
macOS (latest, 3.9, 5.9.*, release)	7m 1s
	1h 2m 22s

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