Cannot update to 20.09

Hello, right now I am on 20.03, trying to update to 20.09.
After nix-channel --add nixos && sudo nixos-rebuild switch --upgrade I have this error:
error: value is a boolean while a set was expected, at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:323:25
What can be wrong? Is it an error in my config?

most likely, an option which was previously just a boolean was made into a set to increase configurability.

you can pass --show-trace to nixos-rebuild to have it output for information. It’s usually noisy, but will state what is going wrong.

Thanks, I found something about my custom not used option in stack trace. After deleting it, update process continued successfully.
Why nixos does not show errors like this in my code in /etc/nixos, but rather shows top of the stack trace somewhere in ./nixos/lib/modules.nix? It’s not very useful or user friendly.

it’s a complex problem, I think there’s some work being done in future nix cli release to improve such error messages