Empty nullable fields are crushed for unknown reason since last 6th in beta version

[adrndfn]

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?

mui

Version

6.0.0-beta.10

Current Behavior

Empty nullable select are crushed for unknown reasons seems last versions

Expected Behavior

Expected behaviour should be input size depends of label when select nullable is empty (no selection)

Steps To Reproduce

1. Using updated mui theme and 6.0.0-beta.10 rjsf version

2. Set a schema with a nullable enum of string (and maybe with other simple type like nullable string to compare render )

        "example-of-enum": {
            "anyOf": [
                {
                    "type": "string",
                    "enum": [
                        "Test1",
                        "Test2",
                    ],
                    "ui:enumNames": [
                        "Test1",
                        "Test2",
                    ]
                },
                {
                    "type": "null",
                    "default": null
                }
            ],
            "title": "Example of enum"
        },
        "example-of-string": {
            "anyOf": [
                {
                    "type": "string"
                },
                {
                    "type": "null",
                    "default": null
                }
            ],
            "title": "Example of string"
        },

3. Use this schema in a uiSchema RJSForm page / react environment

4. Identify crushing problems on nullable empty select mui component ( created from previous string enum nullable ) in comparaison to text field for example.

Environment

- OS: debian
- Node: v22.13.1
- npm: 10.9.2

Anything else?

No response

[heath-freenome]

Here is the playground link for this example. I am wondering what you mean by crushing? In the example playground we are seeing the following where there is no space between the two SelectWidgets:

Is that what you mean?

[adrndfn]

Here is the [playground] link for this example. I am wondering what you mean by crushing? In the example playground we are seeing the following where there is no space between the two SelectWidgets:

Actually I am not really in this example case but more near to something like array example as an array of elements including nullable select.

As you can see on next screenshot, if this default value is empty/null or changing its value on empty/null (no selection) it will make the select empty without value inside, and so field width will be resized:

I do not know why in this example the label do not take the place of the value (even if you can see the label is not completly displayed). But in my case we want to show the label of my field inside it (when null) but it is not completly displayed anymore because of field resize (see next screen).

So why we would expect that input size depends of label when select nullable is empty.
Maybe we didn't see this issue before because field always had an 100% of its parent.
Also knowing our schema use MuiArrayFieldTemplate I am not sure if it is related to @nickgros fix.

Thank's for your time and answer.