Cannot update NULL value in custom module

[textarea]

Preconditions (*)

1. Magento 2.3.4 & 2.4-develop
2. PHP 7.2.27

Steps to reproduce (*)

1. Create a custom module with a field of any data type, for example "varchar", nullable.
2. Insert one record with a (not null) value into the varchar field
3. Update programmatically with null value, i.e.:

$testRepository = $obj->get('\Acme\Test\Api\TestRepositoryInterface');
$test = $testRepository->get(1);
$test->setField(NULL);
$testRepository->save($test);

Expected result (*)

1. Field value is NULL

Actual result (*)

1. Field value still contains the old value

[m2-assistant]

Hi @textarea. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

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• Information on your environment
• Steps to reproduce
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Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento give me 2.4-develop instance - upcoming 2.4.x release

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@textarea do you confirm that you were able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

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[m2-assistant]

Hi @engcom-Hotel. Thank you for working on this issue.
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[magento-engcom-team]

✅ Confirmed by @engcom-Hotel
Thank you for verifying the issue. Based on the provided information internal tickets MC-30919 were created

Issue Available: @engcom-Hotel, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.

[willtran]

FYI can't reproduct on 2.3.3

[textarea]

@willtran I can reproduce this issue on 2.3.3 also.

[engcom-Hotel]

@willtran this issue is reproducible on 2.4-develop