Avoid reading `code` if it doesn't exist #847

Job	Run time
test (3.7, ubuntu-latest)	6m 32s
test (3.8, ubuntu-latest)	4m 42s
test (3.9, ubuntu-latest)	4m 46s
test (3.10, ubuntu-latest)	4m 11s
test (3.11, ubuntu-latest)	2m 53s
test (3.12, ubuntu-latest)	4m 17s
test (3.5, ubuntu-20.04)	6s
test (3.6, ubuntu-20.04)	6m 36s
Finish Coveralls processing	0s
	34m 3s

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