Null Ignoring Weighted Avg ("Wacky") operator in pure postgres

gistfile1.md

Schema (PostgreSQL v12)

        CREATE TABLE test (ts timestamp, value1 float8, value2 float8);
        insert into test values
        ('2017-01-01', 1, 1),
        ('2017-01-02', 1, null),
        ('2017-01-03', 1, 1),
        ('2017-01-04', NULL, 100),
        ('2017-01-05', 1, 1),
        ('2017-01-06', NULL, 1),
        ('2017-01-07', 10, null),
        ('2017-01-09', 1, 1),
        ('2017-01-10', 1, 1),
        ('2017-01-11', NULL, 1),
        ('2017-01-12', NULL, 1);
        
        
        CREATE OR REPLACE FUNCTION wacky_accum_sfunc(accum float8[],numerator float8, denominator float8) RETURNS float8[]
           IMMUTABLE PARALLEL SAFE LANGUAGE sql AS
        $f$
            -- SELECT accum
        	SELECT ARRAY[
        	CASE WHEN denominator is null or numerator is null then accum[1] else accum[1] + numerator END,
        	CASE WHEN denominator is null or numerator is null then accum[2] else accum[2] + denominator END,
            accum[3] + CASE WHEN denominator is null or numerator is null then 0 else 1 END
        	]::float8[]
        $f$;
        
        CREATE OR REPLACE FUNCTION wacky_div(accum float8[]) RETURNS float8[]
           IMMUTABLE PARALLEL SAFE LANGUAGE sql AS
        $f$
        	SELECT ARRAY [
              CASE WHEN accum[2] = 0.0::float8 THEN NULL ELSE accum[1]/accum[2] END,
              accum[3]
            ]
        $f$;
        
        CREATE AGGREGATE wacky(float8, float8) (
        	SFUNC = wacky_accum_sfunc,
        	STYPE = float8[],
            FINALFUNC = wacky_div,
            INITCOND = '{0,0,0}'
        );

---

Query #1

    select 
            wacky(value1, value2), 
            sum(value1)/sum(value2) as naive
        from test;

wacky	naive
1,5	0.14814814814814814

---

View on DB Fiddle

Wacky now returns an array containing N/D where in each slice both N and D were not null, and the number of samples where N and D where both not null

In wacky_div

perhaps this line:

          CASE WHEN accum[2] = 0.0::float8 THEN NULL ELSE accum[1]/accum[2] END,

Should return 0 instead of null, or the line below it should return NULL as well when the line above is null?