Avoid reading `code` if it doesn't exist #851

Job	Run time
test (3.7, ubuntu-latest)	6m 20s
test (3.8, ubuntu-latest)	4m 46s
test (3.9, ubuntu-latest)	4m 47s
test (3.10, ubuntu-latest)	4m 18s
test (3.11, ubuntu-latest)	2m 45s
test (3.12, ubuntu-latest)	4m 27s
test (3.5, ubuntu-20.04)	7s
test (3.6, ubuntu-20.04)	6m 38s
Finish Coveralls processing	0s
	34m 8s

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