BUG#AC-3031: Customer group is NULL for guest orders - issue fixed

Author: glo80326

app/code/Magento/Quote/Model/QuoteManagement.php

@@ -424,8 +424,9 @@ public function placeOrder($cartId, PaymentInterface $paymentMethod = null)
                 }
             }
             $quote->setCustomerIsGuest(true);
-            $groupId = $customer ? $customer->getGroupId() : GroupInterface::NOT_LOGGED_IN_ID;
-            $quote->setCustomerGroupId($groupId);
+            $quote->setCustomerGroupId(
+                $quote->getCustomerId() ? $customer->getGroupId() : GroupInterface::NOT_LOGGED_IN_ID
+            );
         }
 
         $remoteAddress = $this->remoteAddress->getRemoteAddress();

app/code/Magento/Quote/Test/Unit/Model/QuoteManagementTest.php

@@ -240,7 +240,16 @@ protected function setUp(): void
         );
 
         $this->quoteMock = $this->getMockBuilder(Quote::class)
-            ->addMethods(['setCustomerEmail', 'setCustomerGroupId', 'setCustomerId', 'setRemoteIp', 'setXForwardedFor'])
+            ->addMethods(
+                [
+                    'setCustomerEmail',
+                    'setCustomerGroupId',
+                    'setCustomerId',
+                    'getCustomerId',
+                    'setRemoteIp',
+                    'setXForwardedFor',
+                ]
+            )
             ->onlyMethods(
                 [
                     'assignCustomer',
@@ -853,6 +862,7 @@ public function testPlaceOrderIfCustomerIsGuest(): void
         $this->quoteMock->expects($this->any())->method('getBillingAddress')->with()->willReturn($addressMock);
 
         $this->quoteMock->expects($this->once())->method('setCustomerIsGuest')->with(true)->willReturnSelf();
+        $this->quoteMock->expects($this->once())->method('getCustomerId')->willReturn(null);
         $this->quoteMock->expects($this->once())
             ->method('setCustomerGroupId')
             ->with(GroupInterface::NOT_LOGGED_IN_ID);