Intersection of multiple text arrays: ERROR: array value must start with "{" - sql

Question

I'm attemping to get the functions in this question to work: Intersection of multiple arrays in PostgreSQL
Unlike that question, I want to intersect text arrays instead of integer arrays. I've modified both functions accordingly. Base array intersect function:
CREATE FUNCTION array_intersect(a1 text[], a2 text[]) RETURNS text[] AS $$
DECLARE
ret text[];
BEGIN
IF a1 is null THEN
return a2;
ELSEIF a2 is null THEN
RETURN a1;
END IF;
SELECT array_agg(e) INTO ret
FROM (
SELECT unnest(a1)
INTERSECT
SELECT unnest(a2)
) AS dt(e);
RETURN ret;
END;
$$ language plpgsql;
Aggregate function definition:
CREATE AGGREGATE utility.array_intersect_agg(
sfunc = array_intersect,
basetype = text[],
stype = text[],
initcond = NULL
);
I get the error "ERROR: array value must start with "{" or dimension information
SQL state: 22P02" when I try to run the following code:
SELECT array_intersect_agg(test)
FROM(
SELECT ARRAY['A','B','C'] test
UNION ALL
SELECT ARRAY['A','C'] test
) a
What needs to change in order for these functions to work?

Answer 1

For the documentation:
initial_condition
The initial setting for the state value. This must be a string
constant in the form accepted for the data type state_data_type. If
not specified, the state value starts out null.
So the aggregate declaration should look like this:
CREATE AGGREGATE array_intersect_agg(
sfunc = array_intersect,
basetype = text[],
stype = text[]
);