warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
error: cannot coerce a set to a string, at /nix/store/bkbpfnb23ldc2q3mnx8b9mkn2kcys48k-nixos-unstable-2019-04-08/pkgs/build-support/mkshell/default.nix:32:3
(use '--show-trace' to show detailed location information)