Without the change the eval fails as:
$ nix build --no-link -f. diffoscope
error:
… while evaluating the attribute 'drvPath'
at lib/customisation.nix:416:7:
415| // {
416| drvPath =
| ^
417| assert condition;
… while calling the 'derivationStrict' builtin
at <nix/derivation-internal.nix>:34:12:
33|
34| strict = derivationStrict drvAttrs;
| ^
35|
(stack trace truncated; use '--show-trace' to show the full, detailed trace)
error: fetchFromGitHub requires one of either `rev` or `tag` to be provided (not both).
Sergei Trofimovich
4784bc20c8