docs: function ensureExists(path, mask, cb) {
      if (typeof mask == 'function') {
          cb = mask;
          mask = 0777;
      }
  
      filesystem.mkdir(path, mask, function(err) {
          if (err) {
              if (err.code == 'EEXIST') cb(null);
              else cb(err);
          } else cb(null);
      });
  }