Without this fix, I can no longer build anything with releaseTools.nixBuild {}. A job typically fails with:
$ nix-build release.nix -A build.basic.x86_64-linux --show-trace
error: while evaluating the attribute 'lib' of the derivation 'libnixxml-0.1pre1234' at /home/sander/teststuff/nixpkgs/pkgs/build-support/release/nix-build.nix:89:5:
cannot coerce a set to a string, at /home/sander/teststuff/nixpkgs/pkgs/build-support/release/nix-build.nix:89:5
This is caused by the fact that `lib' is propagated as a parameter, which is a function. Functions cannot be converted to strings.
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