Loading
ruby: improve failure message when missing cargoHash
Without this, doing e.g. `pkgs.mkRuby` without a `cargoHash` param would mean that the `fetchCargoTarball` drv was not a FOD and thus had no network access and would give confusing network failure messages. This forces specifying non-null `cargoHash` if it is actually being used, while allowing it to still be `null` when not needed.