code: function _isFilePathVisible(treeData, path) {
          if (path === null) {
              return null;
          } else if (path === "") {
              return true;
          }
  
          var parts = path.split("/"),
              part = parts.shift(),
              result = [],
              node;
  
          while (part) {
              if (treeData === null) {
                  return false;
              }
              node = treeData.get(part);
              if (node === undefined) {
                  return null;
              }
              result.push(part);
              part = parts.shift();
              if (part) {
                  if (!node.get("open")) {
                      return false;
                  }
                  treeData = node.get("children");
                  if (treeData) {
                      result.push("children");
                  }
              }
          }
  
          return true;
      }
docs: @private
  
  See `FileTreeViewModel.isFilePathVisible`