anchor.diff:  
       extraFlags = mkOption {
         type = types.listOf types.str;
  -      default = [];
  +      default = [ ];
         example = [ "--full-if-older-than" "1M" ];
         description = ''
           Extra command-line flags passed to duplicity. See
  
positive.code: { config, lib, pkgs, ...}:
  
  with lib;
  
  let
    cfg = config.services.duplicity;
  
    stateDirectory = "/var/lib/duplicity";
  
    localTarget = if hasPrefix "file://" cfg.targetUrl
      then removePrefix "file://" cfg.targetUrl else null;
  
  in {
    options.services.duplicity = {
      enable = mkEnableOption "backups with duplicity";
  
  
negative.code:     assertions = singleton {
        # Duplicity will fail if the last file selection option is an include. It
        # is not always possible to detect but this simple case can be caught.
        assertion = cfg.include != [ ] -> cfg.exclude != [ ] || cfg.extraFlags != [ ];
        message = ''
          Duplicity will fail if you only specify included paths ("Because the
          default is to include all files, the expression is redundant. Exiting
  