v2: builder fails to produce output path (spring boot)

[0x5a4]

I'm trying to package a spring web app, but it seems the builder fails to produce $out. What am I missing here? I dont have much experience with spring boot myself, so this is even more confusing...

Thanks a lot in advance!

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-24.05";
    gradle2nix.url = "github:tadfisher/gradle2nix/v2";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = {
    self,
    flake-utils,
    gradle2nix,
    ...
  }:
    flake-utils.lib.eachDefaultSystem (
      system: {
        packages.default = gradle2nix.builders.${system}.buildGradlePackage {
          src = ./.;
          pname = "campus-guesser-server";
          version = "1.0";
          lockFile = ./gradle.lock;
          gradleInstallFlags = ["installBootDist"];
        };
      }
    );
}