Define cases when there is a BC break only if experimental feature is enabled.

[Hlavtox]

Prerequisites

• I understand and accept the project's code of conduct.
• I have already searched in existing issues and found no previous report of this bug.

Describe the bug and add attachments

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Expected behavior

No response

Steps to reproduce

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PrestaShop version(s) where the bug happened

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PHP version(s) where the bug happened

No response

Your company or customer's name goes here (if applicable).

No response

[kpodemski]

@Hlavtox could you elaborate? I'm not sure if this is still relevant ?

[Hlavtox]

It's still relevant.

You upgrade to 9.1.
You try the new discount feature.
You create one cart rule using the new discount feature.
You see that it sucks.
You disable the new discount feature.
Your install has BC break because there is NULL in the data that modules don't expect.