private int[][] transformListToIntArray(List<List<Integer>> lists) {
    if (lists.size() <= 1) {
      throw new IllegalStateException(
          "Child size of InnerTimeJoinOperator should be larger than 1.");
    }
    int[][] res = new int[lists.size()][lists.get(0).size()];
    for (int i = 0; i < res.length; i++) {
      List<Integer> list = lists.get(i);
      int[] array = res[i];
      if (list.size() != array.length) {
        throw new IllegalStateException("All child should have same time column result!");
      }
      for (int j = 0; j < array.length; j++) {
        array[j] = list.get(j);
      }
    }
    return res;
  }
Indicate whether we found an empty child input in one loop
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/InnerTimeJoinOperator.java