Number and boolean values in JSON fields break Admin UI
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## Bug report

### Required System information

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- Node.js version: 20.18.1
- NPM version: Yarn 4.6
- Strapi version: 5.6.0
- Database: Postgres
- Operating system: linux/amd64
- Is your project Javascript or Typescript: Typescript

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### Describe the bug

When saving a JSON field with a `number` or `boolean` value, either the following error is displayed:

1. `(config2.doc || "").split is not a function`, when creating a new entry
2. `Cannot read properties of undefined (reading 'length')`, when updating an existing entry

Moreover, when trying to open an entry with an offending value, the first error is displayed.

### Steps to reproduce the behavior

1. Create a new content type with a single json field
2. Create a new entry and enter `42` or `true` into the JSON field
3. Click Publish
4. Lo, an error

### Expected behavior

Expect to see no errors.

### Screenshot

<img width="1442" alt="image" src="https://github.com/user-attachments/assets/b43de5b3-727d-48f8-9e6e-7634820203c3" />

<img width="540" alt="image" src="https://github.com/user-attachments/assets/0b52ff7d-e2cf-4c3a-8667-dcd099e9fd1a" />