Depricated use of null as array offset in php8.5

[victorhjelmbergcego]

https://www.php.net/manual/en/migration85.deprecated.php
"Using null as an array offset or when calling array_key_exists() is now deprecated. Instead an empty string should be used."

This is caused when doing eager loading with single key that is null

class A extends Model
{
    use Compoships;
    
    public function b(): HasMany
    {
        return $this->hasMany(B::class, 'c', 'c');
    }
}

#[Test]
public function bug_reproduction(): void
{
	A::factory()->create(['c' => null]);
	A::query()->with(['b'])->get();
}

The deprication happens in Database/Eloquent/Relations/HasOneOrMany.php where dictKey will be null, which causes array null offset on line 240 in the following