use the default algorithm when set to nullptr #346

Job	Run time
g++-11, Release, Static	3m 29s
g++-11, Release, Shared	3m 49s
clang++-14, Release, Static	3m 31s
clang++-14, Release, Shared	4m 23s
clang++-15, Release, Static	3m 4s
clang++-15, Release, Shared	3m 42s
g++-11, RelWithDebInfo, Static	3m 32s
g++-11, RelWithDebInfo, Shared	4m 7s
clang++-14, RelWithDebInfo, Static	4m 17s
clang++-14, RelWithDebInfo, Shared	3m 55s
clang++-15, RelWithDebInfo, Static	4m 20s
clang++-15, RelWithDebInfo, Shared	3m 5s
	45m 14s

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