PostgreSQL function that returns zero for a zero divisor

postgre.sql

CREATE FUNCTION safe_divide(numeric, numeric) RETURNS numeric AS $$
SELECT
CASE
  WHEN $2 = 0 THEN 0
  ELSE $1/$2
END AS quotient; $$
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;

/**
Usage

SELECT safe_divide(1,0);

Output: 0
**/