public Optional<Expression> getFalseValue() {
    return Optional.ofNullable(falseValue);
  }
IF(v1,v2[,v3]): CASE WHEN v1 THEN v2 [ELSE v3] END
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/sql/ast/IfExpression.java