nix build that fails

test.nix

let
  localPkgs = import <nixpkgs> {};
  # nixos-18.09-small Released on 2019-03-02
  stableRev = "80754f5cfd69d0caf8cff6795d3ce6d99479abde";
  mkNixOSURL = rev:
  "https://github.com/NixOs/nixpkgs-channels/archive/${rev}.tar.gz";
  stableURL = mkNixOSURL stableRev;
  stableBall = fetchTarball {
    url = stableURL;
    sha256 = "1v8g68gqgij389dssh6ry5x1zlhpgcgwjac0rgrh8146gf9hq74f";
  };
  nixopsPkg = builtins.fetchTarball {
    url = "https://github.com/azazel75/nixops/archive/remote-libvirt.tar.gz";
    sha256 = "1mg1bsgwrydyk2i0g5pzc35kr6ybjrihvfns8kd8d6b74qxnyh40";
  };
  remoteVirtNixops = (import "${nixopsPkg}/release.nix" {nixpkgs=stableBall;}).build.${localPkgs.system};
in
  remoteVirtNixops