anchor.diff:  
           serviceConfig =
           {
  -          ExecStart = "${quassel}/bin/quasselcore --listen=${concatStringsSep '','' cfg.interfaces} --port=${toString cfg.portNumber} --configdir=${cfg.dataDir}";
  +          ExecStart = concatStringsSep " " ([
  +            "${quassel}/bin/quasselcore"
  +            "--listen=${concatStringsSep "," cfg.interfaces}"
  +            "--port=${toString cfg.portNumber}"
  +            "--configdir=${cfg.dataDir}"
  +          ] ++ optional cfg.requireSSL "--require-ssl"
  +            ++ optional (cfg.certificateFile != null) "--ssl-cert=${cfg.certificateFile}");
             User = user;
             PermissionsStartOnly = true;
           };
  
positive.code:   ###### implementation
  
    config = mkIf cfg.enable {
  
      users.users = mkIf (cfg.user == null) [
        { name = "quassel";
  
negative.code:         default = false;
          description = ''
            Whether to run the Quassel IRC client daemon.
          '';
        };
  
        certificateFile = mkOption {
          type = types.nullOr types.str;
          default = null;
          description = ''
            Path to the certificate used for SSL connections with clients.
          '';
        };
  
        requireSSL = mkOption {
          type = types.bool;
          default = false;
          description = ''
            Require SSL for connections from clients.
          '';
        };
  
  