fix for empty graph #4

Job	Run time
Build wheels on Linux (aarch64/manylinux)	11m 32s
Build wheels on macOS (arm64)	11m 0s
Build wheels on Linux (x86_64)	24m 13s
Build wheels on macOS (x86_64)	19m 40s
Build wheels for WebAssembly	7m 37s
Build wheels on Linux (aarch64/musllinux)	3m 47s
Build wheels on Windows (ARM64)	27m 42s
Build wheels on Windows (x64)	25m 36s
Build wheels on Windows (Win32)	8m 29s
Build sdist and test extra dependencies	3m 9s
Build with sanitizers for debugging purposes	4m 13s
	2h 26m 58s

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