anchor.diff:  
         user = mkOption {
           default = null;
  +        type = types.nullOr types.str;
           description = ''
             The existing user the Quassel daemon should run as. If left empty, a default "quassel" user will be created.
           '';
  
positive.code: 
        dataDir = mkOption {
          default = "/home/${user}/.config/quassel-irc.org";
          description = ''
            The directory holding configuration files, the SQlite database and the SSL Cert.
          '';
  
negative.code:       };
  
        portNumber = mkOption {
          type = types.port;
          default = 4242;
          description = ''
            The port number the Quassel daemon will be listening to.
  