Merge pull request #3233 from github/mbg/getOptionalEnvVar #1683

Job	Run time
Rust analysis (ubuntu-latest, default)	1m 39s
Rust analysis (ubuntu-latest, linked)	1m 40s
Rust analysis (ubuntu-latest, nightly-latest)	1m 41s
Rust analysis (ubuntu-latest, stable-v2.22.1)	1m 58s
Rust analysis (ubuntu-latest, stable-v2.19.3)	1m 5s
	8m 3s

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