Nix ghc Binary bug

default.nix

let
  defpkgs = builtins.fetchTarball {
    # Descriptive name to make the store path easier to identify
    name = "nixos-22.05.1271.babb041b716";
    # Commit hash for nixos-unstable as of 2018-09-12
    url = "https://releases.nixos.org/nixos/22.05-small/nixos-22.05.1271.babb041b716/nixexprs.tar.xz";
    # Hash obtained using `nix-prefetch-url --unpack <url>`
    sha256 = "0g8vwni83zn6kgkczrm5vwmyhl473rrs9d4k4hn5gfbgfsyv7ls8";
  };
in
{ nixpkgs ? import defpkgs {} }:
let
  src =
    nixpkgs.fetchzip {
      url = "https://github.com/lambdageek/unbound-generics/archive/a2a558058012b09bb313b3eb03cddb734fcf4a98.zip";
      sha256 = "af4592a93d0d280591b3bcff3ebe244956cc3637bf20ed2315fb6b2e070caef4";
    };
  callghcBinary = nixpkgs.haskell.packages.ghc8107Binary.callCabal2nix;
  callghc = nixpkgs.haskell.packages.ghc8107.callCabal2nix;
in callghcBinary "unbound-generics" src {} # this doesn't work
# in callghc "unbound-generics" src {} # this works