docs: public static <T> void putAt(List<T> self, int idx, T value) {
          int size = self.size();
          idx = normaliseIndex(idx, size);
          if (idx < size) {
              self.set(idx, value);
          } else {
              while (size < idx) {
                  self.add(size++, null);
              }
              self.add(idx, value);
          }
      }