message: Fix issue when readme headers are undefined
  Closes
diff: @@ -14,6 +14,7 @@ interface Props {
  const AnchorHeader: React.ElementType = (props: Props) => {
  const value = !isUndefined(props.title) ? props.title : props.children![0].props.value;
  + if (isUndefined(value)) return null;
  const anchor = value
  .trim()
  