[5.6] Implement Optional::__isset

[ghost]

This pull request implemented __isset method on Optional class.
See #24031 for more detail.

[BrandonShar]

I don't understand the example code from your issue. the argument to empty is going to be either a string or null, not an optional. Where is isset being called on the optional?

[ghost]

Because in my example code, the cellphone property is dynamically access from an Optional instace.
The empty structure will do an isset check first, then chek its value.

Check on PHP's document here:

Note:

When using empty() on inaccessible object properties, the __isset() overloading method will be called, if declared.

[BrandonSurowiec]

You can clean up the assertions by using these methods:

$this->assertTrue($value);
$this->assertFalse($value);
$this->assertNull($value);

[ghost]

@BrandonShar Thank you for your advice! I have updated them!

[GrahamCampbell]

invalid syntax

[ghost]

This is auto generated by PhpStorm, I didn't notice that. Since it has been merged, should I open another PR?