⏫ Forwardport of #12241 to 2.3-develop branch

Applied pull request patch https://github.com/magento/magento2/pull/12241.patch (created by @RomaKis) based on commit(s):
  1. ef165a2
  2. f11c0db
  3. 1ebcd7a
  4. a933cf7
  5. f8ed60f

Fixed GitHub Issues in 2.3-develop branch:
  - #10128: New Orders not being saved to order grid (reported by @joergmaertin)

app/code/Magento/Backend/Block/Dashboard/Orders/Grid.php

@@ -92,7 +92,7 @@ protected function _prepareCollection()
     protected function _afterLoadCollection()
     {
         foreach ($this->getCollection() as $item) {
-            $item->getCustomer() ?: $item->setCustomer('Guest');
+            $item->getCustomer() ?: $item->setCustomer($item->getBillingAddress()->getName());
         }
         return $this;
     }

dev/tests/integration/testsuite/Magento/Backend/Block/Dashboard/Orders/GridTest.php

@@ -0,0 +1,44 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\Backend\Block\Dashboard\Orders;
+
+use Magento\Backend\Block\Template\Context;
+
+class GridTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @var Grid
+     */
+    private $block;
+
+    protected function setUp()
+    {
+        parent::setUp();
+
+        $objectManager = \Magento\TestFramework\Helper\Bootstrap::getObjectManager();
+        $block = $this->createMock(\Magento\Backend\Block\Dashboard\Orders\Grid::class);
+        $layout = $this->createMock(\Magento\Framework\View\LayoutInterface::class);
+        $layout->expects($this->atLeastOnce())->method('getChildName')->willReturn('test');
+        $layout->expects($this->atLeastOnce())->method('getBlock')->willReturn($block);
+        $context = $objectManager->create(Context::class, ['layout' => $layout]);
+
+        $this->block = $objectManager->create(Grid::class, ['context' => $context]);
+    }
+
+    /**
+     * @magentoDataFixture Magento/Sales/_files/order.php
+     */
+    public function testGetPreparedCollection()
+    {
+        $collection = $this->block->getPreparedCollection();
+        foreach ($collection->getItems() as $item) {
+            if ($item->getIncrementId() == '100000001') {
+                $this->assertEquals('firstname lastname', $item->getCustomer());
+            }
+        }
+    }
+}