(stack trace truncated; use '--show-trace' to show the full, detailed trace)

error: Refusing to evaluate package 'a-0' in /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-default.nix:12 because it has problems:
- broken: This package is broken.

See also https://nixos.org/manual/nixpkgs/unstable#sec-problems
To allow evaluation regardless, use:
- Nixpkgs import: import nixpkgs { config = <below code>; }
- NixOS: nixpkgs.config = <below code>;
- nix-* commands: Put below code in ~/.config/nixpkgs/config.nix

  {
    problems.handlers = {
      a.broken = "warn"; # or "ignore"
    };
  }