How does LOGICAL_AND function manage NULL values when casting in Bigquery?

Question

I'm using this query to check date fields actually contain dates.

SELECT  id,
ActivityDate 
FROM Database.Table  
WHERE (SELECT LOGICAL_AND(ActivityDate IS NULL OR SAFE_CAST(ActivityDate  AS DATE)
IS NOT NULL ) 
FROM Database.Table)=FALSE;

I know that i have NULLL values so the 'SAFE_CAST(ActivityDate AS DATE) IS NOT NULL ' section of the query should be returning FALSE, and ActivityDate IS NULL should be returning TRUE.

As i understand it because both of the logical operations do not return TRUE i should have some results with FALSE, however i do not.

I'm wondering if this is to do with the safe_cast of the NULL values.

Is it saying the cast has evaluated successfully so therefore it is not NULL?