code: function nextup(inst, orig, argv, event, cb) {
      return function nextupCallback(err, data) {
          if (err) return cb(err, null);
          if (_isQuoted(data)) return cb(null, _unquote(data));
          if (_isValue(data)) return cb(null, _entityToValue(data, inst.library));
          // Remove any nulls or undefineds from the list
          var compact = _compactList(data);
          // Allow the programmer to opt out for _minor_ perf gains
          if (inst.options.doIrreducibleListCheck) {
              // If no change, we'll keep looping forever, so just return
              if (IsEqual(orig, compact)) {
                  Console.printWarning(inst, 'Detected irreducible list; exiting...');
                  return cb(null, compact);
              }
          }
          return exec(inst, compact, argv, event, cb);
      };
  }
docs: Return callback to produce a usable value, or continue execution