Null default value becomes blank string

[damir-manapov]

What you were expecting:
I am expecting to get null value from form state when null default value is set.

What happened instead:
Blank string from form state returns.

Steps to reproduce:

1. Set default field value fo null
2. Get field value

Related code:
Set default value:

<SimpleForm
  defaultValues={{
    field: null,
  }}
>

Use it:

<FormDataConsumer>
  {({formData}) => (
    <div>
      field: {JSON.stringify(formData.field)}
    </div>
  )}
</FormDataConsumer>

Result is:

field: ""

Environment

• React-admin version: 4.4.1
• Last version that did not exhibit the issue (if applicable): 4.3.0
• React version: 18.2.0
• Browser: Chrome 106.0.5249.119

[WiXSL]

Yes. It's a work in progress #8262