@Override
    public Struct get(Object key) {
      if (key instanceof String k) {
        return flatMap(v -> v.get(k.replaceAll("^\\[]\\.?", "")));
      }
      return key instanceof Number n ? get(n.intValue()) : NULL;
    }
Returns a new list where each element of this list has been expanded to the list of elements returned by
{@code mapper}.
<p>
Individual items are treated as a list containing just that item.
planetiler-core/src/main/java/com/onthegomap/planetiler/reader/Struct.java