Postgresql & JSON: ERROR: cannot call json_array_elements on a scalar SQL state: 22023

Trabla: Postgresql: ERROR:  cannot call json_array_elements on a scalar SQL state: 22023

Solving:

This error appears when json is "null" string

SELECT json_array_elements('null'::json)
ERROR:  cannot call json_array_elements on a scalar
********** Error **********

ERROR: cannot call json_array_elements on a scalar
SQL state: 22023

and works fine when correct json array

 SELECT json_array_elements('["a","b","c"]'::json)
Output:
json_array_element  json
------------------------------
""a""
""b""
""c""

To fix  use  'IS NULL' check with CASE
 SELECT 
     CASE 
         WHEN 'null'::json IS NULL 
     THEN '[]'  
END

OR
use replace function with type casting

SELECT
json_array_elements(
         replace(
                         ('null'::json)::character varying,
                         'null',
                         '[]'
        )::json
)