[BUG] - Boolean fields display [object object] with Next.js 15.4+

[vincentwinkel]

Description

This is the (simplified) code:

        createdAt: { formatter: (date) => <span>test</span> },
        isPrivate: { formatter: (bool) => <span>test</span> },

And the result. It looks like the boolean field is broken:

Reproduction URL

null

Reproduction steps

1. I used nextjs 15.2 and nextAdmin 8.1.4, all working perfectly.
2. Then I upgraded to nextjs 15.4, and I noticed an issue on the `formatter` function.
3. I upgraded nextAdmin to 8.3.0 but still the same issue.

Next router

App router

Next Admin version

8.1.4 then 8.3.0

Screenshots

Next Admin options

Logs

Browsers

Chrome

[vincentwinkel]

The same issue seems to occur fot Json fields as well.

[vincentwinkel]

I confirm that there is no issue with nextjs 15.3 (only 15.4).

[foyarash]

Hello @vincentwinkel

Sorry for the delay. I deployed a fix on 8.4.0 that might fix this, could you please try and confirm if that fixes the issue ?

[vincentwinkel]

Sorry also for late reply @foyarash . I'm trying nextjs 15.5.9 (latest 15.* that fixes vulnerabilities) and next-admin 8.4.2, and I get the same issue.
This works:

isPrivate: { formatter: (isPrivate) => (isPrivate ? 'Yes' : 'No') },

But this doesnt work (displays [object Object])

isPrivate: { formatter: (isPrivate) => <span>{isPrivate ? 'Yes' : 'No'}</span> },