Bug: Assigning null to ?array $identities property without proper handling

### PHP Version

8.2.7

### CodeIgniter4 Version

4.6.3

### Shield Version

1.2.0

### Which operating systems have you tested for this bug?

Windows

### Which server did you use?

cli-server (PHP built-in webserver)

### Database

mysqlite(memory unittest)

### Did you customize Shield?

yes:

```php
class User extends \CodeIgniter\Shield\Entities\User
.
.
.
public function saveUsernameIdentity(): bool
{
if (empty($this->username) && empty($this->password) && empty($this->password_hash)) {
return true;
}

/** @var UserIdentityModel $identityModel */
$identityModel = model(UserIdentityModel::class);

$identity = $this->getIdentity('username_password');
if ($identity === null && !empty($this->username)) {
$this->identities = null;

$this->createUsernameIdentity( [
'username' => $this->username,
'password' => '',
]);

$identity = $this->getUsernameIdentity();
}

if ($identity !== null) {
if (!empty($this->username)) {
$identity->secret = $this->username;
}

if (!empty($this->password)) {
$identity->secret2 = service('passwords')->hash($this->password);
}

if (!empty($this->password_hash) && empty($this->password)) {
$identity->secret2 = $this->password_hash;
}

try {
$identityModel->save($identity);
} catch (\CodeIgniter\Database\Exceptions\DataException $e) {
$messages = [
lang('Database.emptyDataset', ['insert']),
lang('Database.emptyDataset', ['update']),
];
if (in_array($e->getMessage(), $messages, true)) {
return true;
}

throw $e;
}
}

return true;
}
```

### What happened?

the `$identities` property is correctly declared as nullable array:
https://github.com/codeigniter4/shield/blob/d07c0f9442dd0712b3fa39bfba677838ff1b8e26/src/Entities/User.php#L50

However, in several places, we directly assign null like these:

https://github.com/codeigniter4/shield/blob/d07c0f9442dd0712b3fa39bfba677838ff1b8e26/src/Entities/User.php#L130

https://github.com/codeigniter4/shield/blob/d07c0f9442dd0712b3fa39bfba677838ff1b8e26/src/Entities/User.php#L149

TypeError: CodeIgniter\Shield\Entities\User::setIdentities(): Argument 1 ($identities) must be of type array, null given,

### Steps to Reproduce

try to reload all identities

### Expected Output

reload identities without error

### Anything else?

_No response_