Can't obtain pessimistic lock when using findOne with where clause based on unique non-primary key

[mivanovaxway]

Describe the bug

I want to lock a row if it matches my search criteria.
(and also prevent such rows from being created while the lock is active).

id is my primary key.
sfdcId is not the primary key but a unique key(varchar).

My code:

let mainProductVersion = await em.findOne(Entities.SfdcProductVersions,
        {'sfdcId': artifactInput.metadata.sfdc_version_id},
        {lockMode: LockMode.PESSIMISTIC_READ});

Debug trace
select e0.* from sfdc_product_versions as e0 where e0.sfdc_id = 'f5DWWDqwDwd2411' limit 1

To Reproduce
Steps to reproduce the behavior:

1. Use findOne with lockMode and query by non-primary key

Expected behavior
The query should contain a lock statement depending on the type of lock such as FOR UPDATE or lock in share mode.

Additional notes
I've tried locking the entity after it's returned, but that does not solve my issue - I want to make sure that
such an entity cannot be created in some other transaction. And since it does not exist at that point ->
I can't lock it.

Versions

Dependency	Version
node	12
typescript	4.1.3
mikro-orm	4.3.4
mysql(server)	5.7

[mivanovaxway]

Update2:
Tested the fix and it works. Thanks.

Update:
@B4nan
I just saw the commit. Thanks a lot. Will test this and write back.