@Override
    public Struct get(Object key) {
      var result = value.get(key);
      if (result != null) {
        return result;
      } else if (key instanceof String s && s.contains(".")) {
        String[] parts = s.split("\\.", 2);
        if (parts.length == 2) {
          String firstPart = parts[0];
          return firstPart.endsWith("[]") ?
            get(firstPart.substring(0, firstPart.length() - 2)).flatMap(child -> child.get(parts[1])) :
            get(firstPart, parts[1]);
        }
      }

      return 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