MAGETWO-58393: An error occurs while saving configurable product

app/code/Magento/ConfigurableProduct/Model/Product/VariationHandler.php

@@ -148,10 +148,14 @@ class VariationHandler
         \Magento\Catalog\Model\Product $parentProduct,
         $postData
     ) {
+        $typeId = isset($postData['weight']) && !empty($postData['weight'])
+            ? ProductType::TYPE_SIMPLE
+            : ProductType::TYPE_VIRTUAL;
+
         $product->setStoreId(
             \Magento\Store\Model\Store::DEFAULT_STORE_ID
         )->setTypeId(
-            $postData['weight'] ? ProductType::TYPE_SIMPLE : ProductType::TYPE_VIRTUAL
+            $typeId
         )->setAttributeSetId(
             $parentProduct->getNewVariationsAttributeSetId()
         );

app/code/Magento/ConfigurableProduct/Test/Unit/Model/Product/VariationHandlerTest.php

@@ -8,6 +8,7 @@
 
 namespace Magento\ConfigurableProduct\Test\Unit\Model\Product;
 
+use Magento\Catalog\Model\Product\Type;
 use Magento\ConfigurableProduct\Model\Product\VariationHandler;
 
 /**
@@ -162,23 +163,30 @@ class VariationHandlerTest extends \PHPUnit_Framework_TestCase
 
     /**
      * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
+     * @dataProvider dataProviderTestGenerateSimpleProducts
+     * @param int|string|null $weight
+     * @param string $typeId
      */
-    public function testGenerateSimpleProducts()
+    public function testGenerateSimpleProducts($weight, $typeId)
     {
         $productsData = [
-            6 =>
-                [
-                    'image' => 'image.jpg',
-                    'name' => 'config-red',
-                    'configurable_attribute' => '{"new_attr":"6"}',
-                    'sku' => 'config-red',
-                    'quantity_and_stock_status' =>
-                        [
-                            'qty' => '',
-                        ],
-                    'weight' => '333',
-                ]
+            [
+                'image' => 'image.jpg',
+                'name' => 'config-red',
+                'configurable_attribute' => '{"new_attr":"6"}',
+                'sku' => 'config-red',
+                'quantity_and_stock_status' =>
+                    [
+                        'qty' => '',
+                    ],
+            ]
         ];
+
+        // Do not add 'weight' attribute if it's value is null!
+        if ($weight !== null) {
+            $productsData[0]['weight'] = $weight;
+        }
+
         $stockData = [
             'manage_stock' => '0',
             'use_config_enable_qty_increments' => '1',
@@ -218,7 +226,7 @@ class VariationHandlerTest extends \PHPUnit_Framework_TestCase
             )
             ->disableOriginalConstructor()
             ->getMock();
-        $productTypeMock = $this->getMockBuilder(\Magento\Catalog\Model\Product\Type::class)
+        $productTypeMock = $this->getMockBuilder(Type::class)
             ->setMethods(['getSetAttributes'])
             ->disableOriginalConstructor()
             ->getMock();
@@ -236,7 +244,7 @@ class VariationHandlerTest extends \PHPUnit_Framework_TestCase
             ->willReturn('new_attr_set_id');
         $this->productFactoryMock->expects($this->once())->method('create')->willReturn($newSimpleProductMock);
         $newSimpleProductMock->expects($this->once())->method('setStoreId')->with(0)->willReturnSelf();
-        $newSimpleProductMock->expects($this->once())->method('setTypeId')->with('simple')->willReturnSelf();
+        $newSimpleProductMock->expects($this->once())->method('setTypeId')->with($typeId)->willReturnSelf();
         $newSimpleProductMock->expects($this->once())
             ->method('setAttributeSetId')
             ->with('new_attr_set_id')
@@ -265,6 +273,27 @@ class VariationHandlerTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals(['product_id'], $this->model->generateSimpleProducts($parentProductMock, $productsData));
     }
 
+    /**
+     * @return array
+     */
+    public function dataProviderTestGenerateSimpleProducts()
+    {
+        return [
+            [
+                'weight' => 333,
+                'type_id' => Type::TYPE_SIMPLE,
+            ],
+            [
+                'weight' => '',
+                'type_id' => Type::TYPE_VIRTUAL,
+            ],
+            [
+                'weight' => null,
+                'type_id' => Type::TYPE_VIRTUAL,
+            ],
+        ];
+    }
+
     public function testProcessMediaGalleryWithImagesAndGallery()
     {
         $this->product->expects($this->atLeastOnce())->method('getMediaGallery')->with('images')->willReturn([]);