@otini Nix (Expression Language) errors are *terrible* (which is expected because of lack of an advance type system) but *also* Nix is a DSL so lacks tools to debug issues. In conclusion the situation is even more terrible than only terrible.
Community is trying to improve the state of the things¹² but it is nothing serious.
¹ www.haskellforall.com/2017/01/typed-nix-programming-using-dhall.html
² https://www.gofundme.com/typing-nix