message: fix: check if searchText is null
diff: const children = get(item, childrenField) || [];
  const title = get(item, titleField);
  - const searchIdx = title.indexOf(searchText);
  + const searchIdx = searchText ? title.indexOf(searchText) : -1;
  const isHighlight =
  searchState.startSearch && !isEmpty(searchText) && highlight && searchIdx !== -1;
  const highlightStyle = `color: ${isBoolean(highlight) ? '#f50' : highlight}`;
  