[5.x] Fix isset and empty on Values (#12865)

Co-authored-by: Jason Varga <[email protected]>

Author: edalzell

src/Fields/Values.php

@@ -79,6 +79,11 @@ public function raw($key)
         return $value instanceof Value ? $value->raw() : $value;
     }
 
+    public function __isset($key)
+    {
+        return $this->offsetExists($key);
+    }
+
     public function __get($key)
     {
         return $this->offsetGet($key);

tests/Fields/ValuesTest.php

@@ -148,6 +148,10 @@ public function property_access()
             'charlie' => new Value('delta', null, $this->fieldtype),
         ]);
 
+        $this->assertTrue(isset($values->alfa));
+        $this->assertFalse(empty($values->alfa));
+        $this->assertFalse(isset($values->missing));
+        $this->assertTrue(empty($values->missing));
         $this->assertEquals('bravo', $values->alfa);
         $this->assertEquals('delta (augmented)', $values->charlie);
         $this->assertIsString($values->charlie);
@@ -274,6 +278,7 @@ public function augment($ids)
 class TestAugmentableObject implements Augmentable
 {
     use HasAugmentedData;
+
     protected $data = [];
 
     public function __construct($data)