BUG #16549: "CASE" not work properly , the function works properly on PostgreSQL 9.6.8

The following bug has been logged on the website:

Bug reference:      16549
Logged by:          Sławomir Nowakiewicz
Email address:      slawomir.nowakiewicz@rubix.com
PostgreSQL version: 12.1
Operating system:   Linux
Description:

"CASE" try to cast a string to integer when a condition is not met. I
checked this function also on PostgreSQL 11.2 - the result is the same.

BEGIN;
CREATE TABLE public.temp_data_type
(
    data_type_name text NOT NULL,
    data_type_storage_type text NOT NULL DEFAULT ''::text
);

INSERT INTO public.temp_data_type
VALUES 
('INTEGER','int'),
('LOOKUP_TABLE','string');

CREATE OR REPLACE FUNCTION public.temp_item_attribute_create(p_datatype
text, p_values text[])
    RETURNS integer
    LANGUAGE 'plpgsql'
    VOLATILE 
    
AS $BODY$
DECLARE
    value_int integer;
    i integer;
BEGIN
        i:=1;
        --RAISE NOTICE 'datatype: %', p_datatype;    
        --RAISE NOTICE 'attribute.values[i]: %',p_values[i];    
                
        value_int := CASE WHEN p_datatype::TEXT IN (SELECT data_type_name FROM
temp_data_type WHERE data_type_storage_type = 'int') THEN 
                                        p_values[i]::INTEGER
                                    ELSE 
                                        NULL::INTEGER
                                    END;
                
    
                            
    RETURN value_int;
END;
$BODY$;

ALTER FUNCTION public.temp_item_attribute_create(text,text[])
    OWNER TO postgres;

SELECT temp_item_attribute_create('LOOKUP_TABLE','{SHELL}');
--ROLLBACK;



ERROR:  22P02: invalid input syntax for type integer: "SHELL"
CONTEXT:  SQL statement "SELECT CASE WHEN p_datatype::TEXT IN (SELECT
data_type_name FROM temp_data_type WHERE data_type_storage_type = 'int')
THEN

   p_values[i]::INTEGER

ELSE

   NULL::INTEGER

END"
PL/pgSQL function temp_item_attribute_create(text,text[]) line 10 at
assignment
LOCATION:  pg_strtoint32, numutils.c:259