BigQuery standard SQL : checking if an array is null does not work

Question

If i launch this query :

with a as (
select cast(null as array<string>) as x union all select ['str1','str2'] as x)
select * from a where x is null

I get this result :

This is the result i expected.

But if i first launch this query :

 select cast(null as array<string>) as x union all select ['str1', 'str2'] as x

whose result i save in a table "a" in a dataset "tmp" and then i launch this query :

select * from `tmp.a` where x is null

I get this result :

I expected a result identical to the first one. Why is there a difference between the two results ?

Answer 1

Workaround : To get the same result for both cases you could use in your where clause the function ARRAY_LENGTH(x)=0.