code: function _moveMarker(treeData, markerName, oldPath, newPath) {
          var objectPath;
  
          if (newPath) {
              objectPath = _filePathToObjectPath(treeData, newPath);
          }
  
          var newTreeData = treeData;
  
          if (oldPath && oldPath !== newPath) {
              var lastObjectPath = _filePathToObjectPath(treeData, oldPath);
              if (lastObjectPath) {
                  newTreeData = newTreeData.updateIn(lastObjectPath, function (entry) {
                      return entry.delete(markerName);
                  });
              }
          }
  
          if (newPath && objectPath && objectPath.length !== 0) {
              newTreeData = newTreeData.updateIn(objectPath, function (entry) {
                  return entry.set(markerName, true);
              });
          }
  
          return newTreeData;
      }
docs: @private
  
  See `FileTreeViewModel.moveMarker`