string cast array missing null value

[cxzl25]

Describe the bug

To Reproduce

spark-sql (default)> select * from test_t1 ;
NULL

set spark.auron.enable=true;
select cast(array(c1) as string ) from test_t1 ;

[]

---

set spark.auron.enable=false;
set spark.sql.legacy.castComplexTypesToString.enabled=false;
select cast(array(c1) as string ) from test_t1 ;

[null]

Expected behavior

Screenshots

Additional context