[8.x] Fix fail to morph with custom casting to objects

src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php

@@ -256,7 +256,7 @@ public function morphTo($name = null, $type = null, $id = null, $ownerKey = null
         // If the type value is null it is probably safe to assume we're eager loading
         // the relationship. In this case we'll just pass in a dummy query where we
         // need to remove any eager loads that may already be defined on a model.
-        return is_null($class = $this->{$type})
+        return is_null($class = $this->getAttributeFromArray($type))
                     ? $this->morphEagerTo($name, $type, $id, $ownerKey)
                     : $this->morphInstanceTo($class, $name, $type, $id, $ownerKey);
     }

tests/Database/DatabaseEloquentModelTest.php

@@ -1275,6 +1275,7 @@ public function testMorphToCreatesProperRelation()
         $this->addMockConnection($model);
 
         // $this->morphTo();
+        $model->setAttribute('morph_to_stub_type', EloquentModelSaveStub::class);
         $relation = $model->morphToStub();
         $this->assertSame('morph_to_stub_id', $relation->getForeignKeyName());
         $this->assertSame('morph_to_stub_type', $relation->getMorphType());
@@ -2229,7 +2230,6 @@ class EloquentModelStub extends Model
     public $scopesCalled = [];
     protected $table = 'stub';
     protected $guarded = [];
-    protected $morph_to_stub_type = EloquentModelSaveStub::class;
     protected $casts = ['castedFloat' => 'float'];
 
     public function getListItemsAttribute($value)

tests/Database/DatabaseEloquentMorphToTest.php

@@ -92,8 +92,8 @@ public function testMorphToWithArrayDefault()
 
     public function testMorphToWithZeroMorphType()
     {
-        $parent = $this->getMockBuilder(EloquentMorphToModelStub::class)->onlyMethods(['getAttribute', 'morphEagerTo', 'morphInstanceTo'])->getMock();
-        $parent->method('getAttribute')->with('relation_type')->willReturn(0);
+        $parent = $this->getMockBuilder(EloquentMorphToModelStub::class)->onlyMethods(['getAttributeFromArray', 'morphEagerTo', 'morphInstanceTo'])->getMock();
+        $parent->method('getAttributeFromArray')->with('relation_type')->willReturn(0);
         $parent->expects($this->once())->method('morphInstanceTo');
         $parent->expects($this->never())->method('morphEagerTo');