[9.x] Remove null default attributes names when UPDATED_AT or CREATED_AT is null at Model::replicate

[mazinsw]

framework/src/Illuminate/Database/Eloquent/Model.php

Line 1606 in d425952

$this->getUpdatedAtColumn(),

Generates on PHP 8.0
PHP Deprecated: explode(): Passing null to parameter #2 ($string) of type string is deprecated

Example:

class Order extends Model
{
    public const CREATED_AT = 'created_at';
    public const UPDATED_AT = null;

Code at database Model:

    public function replicate(array $except = null)
    {
        $defaults = [
            $this->getKeyName(),
            $this->getCreatedAtColumn(),
            $this->getUpdatedAtColumn(), // <---- null here
        ];

        $attributes = Arr::except( // <-- call Arr::forget
            $this->getAttributes(), $except ? array_unique(array_merge($except, $defaults)) : $defaults
        );

Trigger warning at Arr::forget:

public static function forget(&$array, $keys)
    {
        ...
        foreach ($keys as $key) {
            ...
            $parts = explode('.', $key); // <-- $key is null where but explode requires strict string type (null not allowed)