@SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "intended")
  public List<ExpressionTree> getChildren() {
    return children;
  }
Generate the old string for the old test cases.
@return the expression as a string using the leaf ids
storage-api/src/java/org/apache/hadoop/hive/ql/io/sarg/ExpressionTree.java