React warning for update forms

### Before opening, please confirm:

- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-adminui/issues?q=is%3Aissue+).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-adminui/blob/main/CONTRIBUTING.md#bug-reports).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.
- [X] I have removed any sensitive information from my code snippets and submission.

### App Id

n/a

### Region

n/a

### Environment name

n/a

### Figma File Version (if applicable)

_No response_

### Amplify CLI Version

_No response_

### If applicable, what version of Node.js are you using?

_No response_

### What operating system are you using?

_No response_

### Browser type?

_No response_

### Describe the bug

If I have the following schema:
```
type Cat @model {
name: String
age: Int
}
```

and save a Cat with no name (I can because it's an optional field)
and then try to update the Cat with an auto-generated UpdateCatForm,
I get the following warning in the console:

```
A component is changing a controlled input to be uncontrolled. This is likely caused by the value changing from a defined to undefined, which should not happen. Decide between using a controlled or uncontrolled input element for the lifetime of the component.
```

### Expected behavior

The form should handle nullish values coming from Dynamo gracefully.

### Reproduction steps

See description.

### Project Identifier

_No response_

### Additional information

_No response_

Start by reproducing the schema and generated UpdateCatForm described in the issue, then inspect how optional nullish values from Dynamo are passed to the form inputs. Done means updating a Cat saved without a name no longer produces the controlled-input warning.

Written by the indexing model from the issue text.