Avoid reading `code` if it doesn't exist #849

Job	Run time
test (3.7, ubuntu-latest)	6m 58s
test (3.8, ubuntu-latest)	4m 45s
test (3.9, ubuntu-latest)	4m 44s
test (3.10, ubuntu-latest)	4m 13s
test (3.11, ubuntu-latest)	2m 49s
test (3.12, ubuntu-latest)	4m 18s
test (3.5, ubuntu-20.04)	7s
test (3.6, ubuntu-20.04)	6m 36s
Finish Coveralls processing	0s
	34m 30s

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