Optional should implement __isset

[ghost]

• Laravel Version: 5.6
• PHP Version: 7.2
• Database Driver & Version: No Database

Description:

\Illuminate\Support\Optional should implement __isset, there are some cases that maight need this.
For example, I have an Eloquent HasMany relation, say contacts on model User:

<?php
$user = User::find(1);
$hasPhoneNumber = !empty(optional($user->contacts->first())->cellphone);

$user->contacts maight be an empty Collection, so I have to check it by optional helper.
Since the Optional didn't implement __isset, $hasPhoneNumber will always be false.

Steps To Reproduce:

See code above.

[tillkruss]

Feel free to submit a pull request.