MySQL JSON_EXTRACT subquery not working when enclosed in IFNULL

Goal
Select a value based on a value returned by a subquery that is using JSON_EXTRACT which either returns a 'value' or NULL. IFNULL should be able to allow you to set a default value when the JSON_EXTRACT does not return a result.

Problem
When using a subquery that uses JSON_EXTRACT and returns a result, will return nothing when enclosed in IFNULL ignoring the default value.

Consider the following case
We want to select a SubscriptionPlan.name based on an identifier that is the result of a subquery using JSON_EXTRACT.

SELECT 
    subscriptionplan.name
FROM
    SubscriptionPlan AS subscriptionplan
WHERE
    subscriptionplan.identifier = (
                        SELECT 
                            JSON_EXTRACT(product.data, '$.identifier')
                        FROM
                            Subscription AS subscription
                        JOIN
                            Product AS product ON product.productid = subscription.productid
                        WHERE
                            subscription.status = 'ACTIVE'
                        AND
                            subscription.ownerid = :userId
                    )

Case 1. SUCCESS without IFNULL

Subscription exists with status 'ACTIVE' and 'userId'
- Subquery result: 'PRO' and thus finds the SubscriptionPlan
- Final result: 'Professional'

Case 2. NOT FOUND without IFNULL

Subscription not found with status 'ACTIVE' and 'userId'
- Subquery result: NULL and thus does not find a SubscriptionPlan
- Final result: NULL

Now we add the IFNULL operation to default to 'FREE' subscription plan:

subscriptionplan.identifier = IFNULL(
                                  ( SELECT JSON_EXTRACT ... ),
                                  'FREE'
                              )

Case 3. SUCCESS with IFNULL

Subscription exists with status 'ACTIVE' and 'userId'
 - Subquery result: NULL even though the subscription was found !???
 - Final result: NULL

Case 4. NOT FOUND with IFNULL

Subscription not found with status 'ACTIVE' and 'userId'
 - Subquery result: FREE and thus finds the FREE SubscriptionPlan
 - Final result: 'Free'

The IFNULL expression nullifies the subquery result, and it does not default to 'FREE'.

My thoughts are as follows:

• Case 4: is using the IFNULL default value string 'FREE' and therefore works as intended
• Case 3: subquery should return PRO and even if it returns NULL, it should default to 'FREE', neither happens
• Maybe adding the IFNULL query adds another nesting layer where

What i've tried and did not work:

• IF( () IS NULL, 'do stuff', 'do other stuff')
• IF( ISNULL(<query<), 'do stuff', 'do other stuff')
• IF( () = null , ..., ...)
• IF( () = NULL , ..., ...)
• IF( () = 'null' , ..., ...)
• IF( () = 'NULL' , ..., ...)

Also according to Can't detect null value from JSON_EXTRACT:

• IF ( JSON_EXTRACT(product.data, '$.identifier') = CAST('null' AS JSON), ...., ... )

All failures! Why is JSON_EXTRACT subquery not working when enclosed in IFNULL?