Inconsistent defaultFormState for arrays

[HanLap]

Prerequisites

• I have searched the existing issues
• I understand that providing a SSCCE example is tremendously useful to the maintainers.
• I have read the documentation
• Ideally, I'm providing a sample JSFiddle, Codesandbox.io or preferably a shared playground link demonstrating the issue.

What theme are you using?

other

Version

6.6.2

Current Behavior

While updating from 5.x to 6.x, I noticed changed behavior with the default form state for arrays.

In 5.24.13 array fields were always initialized with an empty array.
In 6.6.2 this no longer is the case.

The only hint I could find that this change was intentional, is in #4798

Updated getDefaultFormState to fix an issue where optional array props had their default set to an empty array when they shouldn't be

Furthermore, I noticed that setting experimental_defaultFormStateBehavior.arrayMinItems.populate to never, will restore the previous behavior of always defaulting to an empty array. This seems inconsistent to me.

Expected Behavior

Since, this change is not properly documented in the upgrade guide for 6.x, I'd like some clarification on the intended behavior here.

If the expected behavior is to keep arrays unset by default, I would love to have a config option to control this behavior.

Steps To Reproduce

Here are two sandboxes, demonstrating the behavior in 5.x and 6.x:

• 5.24.13
• 6.6.2

Environment

- OS: Ubuntu 22.04
- Node: 24.14.0
- pnpm: 11.9.0

Anything else?

No response

[heath-freenome]

@HanLap It was definitely intentional. If the array is optional then it should not default to an empty array. You found a bug with experimental_defaultFormStateBehavior.arrayMinItems.populate = never. We'll go about fixing that. We will also update the v6 migration guide to highlight this bug fix.

Sounds like you were relying on the bug where optional arrays were defaulted to empty as a feature? If you really need the new feature for the restoration of the bug behavior, then please file a new issue so that we can focus on that independently of the documentation and defaulting bug you reported.

[HanLap]

Sounds good to me! Thank you 🙂

I'll talk it over with my team again and create a separate issue if we come to the conclusion that we really cannot risk this change in behavior.