Using THETA_SKETCH SQL Functions

I am having trouble trying to use the THETA_SKETCH_INTERSECT Druid SQL function

Reading the docs, it seems straightforward:

Syntax:

THETA_SKETCH_INTERSECT([size], expr0, expr1, …)

Returns an intersection of theta sketches, where each input expression must return a theta sketch. The size can be optionally specified as the first parameter.

Having read that, I tried to create my SQL snippet, basically I am trying to get the number of common customers between two stores in my datasource my_table:

SELECT THETA_SKETCH_INTERSECT( ( SELECT DISTINCT_CUSTOMERS FROM my_table WHERE var1 = 'STORE_A' ), ( SELECT DISTINCT_CUSTOMERS FROM my_table WHERE var1 = 'STORE_B' ) )

Running that leads me to this error:

Unknown exception / Cannot build plan for query: SELECT THETA_SKETCH_INTERSECT( (SELECT DISTINCT_CUSTOMERS FROM tm_agg WHERE STORE = 'STOR_WATS'), (SELECT DISTINCT_CUSTOMERS FROM tm_agg WHERE STORE = 'STOR_ACEH') ) / org.apache.druid.java.util.common.ISE

Hope anyone can help me on this.

Note: I know that Native query is easier. But I have my limitations and would appreciate if I can make the THETA_SKETCH functions work via SQL. Thanks!