protected boolean canSkipCurrentChild(int currentChildIndex) {
    return !isEmpty(currentChildIndex) || children.get(currentChildIndex) == null;
  }
@param currentChildIndex the index of the child
@return true if we can skip the currentChild in prepareInput
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/AbstractConsumeAllOperator.java