Output path comparison

error: while evaluating anonymous function at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/.gc-of-borg-outpaths.nix:35:12, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/attrsets.nix:199:52:
while evaluating the attribute ‘x86_64-darwin’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/attrsets.nix:185:41:
while evaluating anonymous function at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/top-level/release-lib.nix:66:6, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/attrsets.nix:282:43:
while evaluating ‘hydraJob’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:157:14, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/top-level/release-lib.nix:66:14:
while evaluating the attribute ‘drvPath’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:174:13:
while evaluating the attribute ‘drvPath’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:145:40:
while evaluating the attribute ‘stdenv’ of the derivation ‘2bwm-0.2’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/generic/make-derivation.nix:98:11:
while evaluating the attribute ‘preHook’ of the derivation ‘stdenv-darwin’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/generic/default.nix:72:14:
while evaluating the attribute ‘darwin.CF’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/os-specific/darwin/apple-source-releases/default.nix:199:5:
while evaluating ‘callPackageWith’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:113:35, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/os-specific/darwin/apple-source-releases/default.nix:199:23:
while evaluating ‘makeOverridable’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:72:24, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:117:8:
while evaluating anonymous function at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/os-specific/darwin/apple-source-releases/CF/default.nix:1:1, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/lib/customisation.nix:74:12:
while evaluating the attribute ‘cc.isClang’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/generic/default.nix:137:14:
while evaluating anonymous function at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/build-support/cc-wrapper/default.nix:8:1, called from /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/darwin/default.nix:81:49:
while evaluating the attribute ‘nativeBuildInputs’ of the derivation ‘Libsystem-osx-10.11.6’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/generic/make-derivation.nix:98:11:
while evaluating the attribute ‘src’ of the derivation ‘cpio-2.12’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/generic/make-derivation.nix:98:11:
while evaluating the attribute ‘curlVersion’ of the derivation ‘cpio-2.12.tar.bz2’ at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/stdenv/generic/make-derivation.nix:98:11:
attribute ‘version’ missing, at /var/lib/gc-of-borg/.nix-test-rs/repo/38dca4e3aa6bca43ea96d2fcc04e8229/mr-est/grahamc-zoidberg/pkgs/build-support/fetchurl/default.nix:135:17