Cannot update null value into nullable field using UPDATE JOIN JSON_TABLE

Question

I create table TABLE_A with column "product_value" type decimal(11,2) NULLABLE and try update using JSON_TABLE as follow

UPDATE TABLE_A src 
JOIN JSON_TABLE("[{\"id\":1,\"product_value\":null}]",'$[*]' COLUMNS 
(id int(11) PATH '$.\"id\"',
product_value decimal(11,2) PATH '$.\"product_value\"' NULL ON EMPTY)) as target 
ON src.id = target.id 

SET 
src.product_value = null
where src.id = 1;

I got the error

Invalid JSON value for CAST to DECIMAL from column product_value

Why I cannot set null to column product_value when using JOIN JSON_TABLE?

But I can update this field to NULL by this command:

UPDATE TABLE_A src 
JOIN  TABLE_B as target ON src.u_id = target.u_id 
SET src.product_value = null
WHERE src.id = 1

The result had no error.

Both sql update the SAME column to NULL. But the sql with JSON_TABLE has error. Do you have any suggestion?