diff --git a/app/code/Magento/Customer/Model/Customer.php b/app/code/Magento/Customer/Model/Customer.php
index 81ea34e6f9430..8c7f3e1661fcd 100644
--- a/app/code/Magento/Customer/Model/Customer.php
+++ b/app/code/Magento/Customer/Model/Customer.php
@@ -357,7 +357,7 @@ public function getDataModel()
             \Magento\Customer\Api\Data\CustomerInterface::class
         );
         $customerDataObject->setAddresses($addressesData)
-            ->setId($this->getId() ? (int) $this->getId() : null);
+            ->setId($this->getId());
         return $customerDataObject;
     }
 
diff --git a/app/code/Magento/Persistent/Model/Plugin/ConvertCustomerCartToGuest.php b/app/code/Magento/Persistent/Model/Plugin/ConvertCustomerCartToGuest.php
index 3e4b005db8930..862414cacded8 100644
--- a/app/code/Magento/Persistent/Model/Plugin/ConvertCustomerCartToGuest.php
+++ b/app/code/Magento/Persistent/Model/Plugin/ConvertCustomerCartToGuest.php
@@ -24,6 +24,9 @@
 use Magento\Quote\Model\Quote;
 use Magento\Quote\Model\QuoteManagement;
 
+/**
+ * @SuppressWarnings(PHPMD.CookieAndSessionMisuse)
+ */
 class ConvertCustomerCartToGuest
 {
     /**
diff --git a/app/code/Magento/Persistent/Model/QuoteManager.php b/app/code/Magento/Persistent/Model/QuoteManager.php
index 7c7433aa2263e..4485240650cd7 100644
--- a/app/code/Magento/Persistent/Model/QuoteManager.php
+++ b/app/code/Magento/Persistent/Model/QuoteManager.php
@@ -23,22 +23,16 @@
 class QuoteManager
 {
     /**
-     * Persistent session
-     *
      * @var \Magento\Persistent\Helper\Session
      */
     protected $persistentSession;
 
     /**
-     * Checkout session
-     *
      * @var \Magento\Checkout\Model\Session
      */
     protected $checkoutSession;
 
     /**
-     * Persistent data
-     *
      * @var Data
      */
     protected $persistentData;
diff --git a/app/code/Magento/Persistent/Test/Unit/Model/QuoteManagerTest.php b/app/code/Magento/Persistent/Test/Unit/Model/QuoteManagerTest.php
index a30f0755fa951..d239c9096f050 100644
--- a/app/code/Magento/Persistent/Test/Unit/Model/QuoteManagerTest.php
+++ b/app/code/Magento/Persistent/Test/Unit/Model/QuoteManagerTest.php
@@ -343,30 +343,38 @@ public function testExpire(): void
      */
     public function testConvertCustomerCartToGuest(): void
     {
-        $quoteId = 1;
         $addressArgs = ['customerAddressId' => null];
         $customerIdArgs = ['customerId' => null];
-        $emailArgs = ['email' => null];
-
-        $this->checkoutSessionMock->expects($this->once())
-            ->method('getQuoteId')->willReturn($quoteId);
-        $this->quoteMock->expects($this->once())->method('getId')->willReturn($quoteId);
-        $this->quoteRepositoryMock->expects($this->once())->method('get')->with($quoteId)->willReturn($this->quoteMock);
+        $email = 'test@example.com';
+        $firstname = 'Firstname';
+        $lastname = 'Lastname';
+
+        $billingAddressMock = $this->createMock(Address::class);
+        $billingAddressMock->method('getEmail')->willReturn($email);
+        $billingAddressMock->method('getFirstname')->willReturn($firstname);
+        $billingAddressMock->method('getLastname')->willReturn($lastname);
+        $this->quoteMock->method('getBillingAddress')->willReturn($billingAddressMock);
         $this->quoteMock->expects($this->once())
-            ->method('setIsActive')->with(true)->willReturn($this->quoteMock);
+            ->method('setCustomerId')
+            ->with(null)
+            ->willReturn($this->quoteMock);
         $this->quoteMock->expects($this->once())
-            ->method('setCustomerId')->with(null)->willReturn($this->quoteMock);
+            ->method('setCustomerEmail')->with($email)
+            ->willReturn($this->quoteMock);
         $this->quoteMock->expects($this->once())
-            ->method('setCustomerEmail')->with(null)->willReturn($this->quoteMock);
+            ->method('setCustomerFirstname')
+            ->with($firstname)
+            ->willReturn($this->quoteMock);
         $this->quoteMock->expects($this->once())
-            ->method('setCustomerFirstname')->with(null)->willReturn($this->quoteMock);
+            ->method('setCustomerLastname')->with($lastname)
+            ->willReturn($this->quoteMock);
         $this->quoteMock->expects($this->once())
-            ->method('setCustomerLastname')->with(null)->willReturn($this->quoteMock);
-        $this->quoteMock->expects($this->never())->method('setCustomerGroupId')
+            ->method('setCustomerGroupId')
+            ->with(0)
             ->willReturn($this->quoteMock);
         $this->quoteMock->expects($this->once())
             ->method('setIsPersistent')->with(false)->willReturn($this->quoteMock);
-        $this->quoteMock->expects($this->exactly(3))
+        $this->quoteMock->expects($this->exactly(2))
             ->method('getAddressesCollection')->willReturn($this->abstractCollectionMock);
         $customerMock = $this->createMock(CustomerInterface::class);
         $customerMock->expects($this->once())
@@ -375,49 +383,18 @@ public function testConvertCustomerCartToGuest(): void
             ->willReturnSelf();
         $this->quoteMock->expects($this->once())
             ->method('getCustomer')->willReturn($customerMock);
-        $this->abstractCollectionMock->expects($this->exactly(3))->method('walk')->with(
+        $this->abstractCollectionMock->expects($this->exactly(2))->method('walk')->with(
             $this->logicalOr(
                 $this->equalTo('setCustomerAddressId'),
                 $this->equalTo($addressArgs),
                 $this->equalTo('setCustomerId'),
-                $this->equalTo($customerIdArgs),
-                $this->equalTo('setEmail'),
-                $this->equalTo($emailArgs)
+                $this->equalTo($customerIdArgs)
             )
         );
         $this->quoteMock->expects($this->once())->method('collectTotals')->willReturn($this->quoteMock);
-        $this->persistentSessionMock->expects($this->once())
-            ->method('getSession')->willReturn($this->sessionMock);
-        $this->sessionMock->expects($this->once())
-            ->method('removePersistentCookie')->willReturn($this->sessionMock);
         $this->quoteRepositoryMock->expects($this->once())->method('save')->with($this->quoteMock);
 
-        $this->model->convertCustomerCartToGuest();
-    }
-
-    /**
-     * @return void
-     */
-    public function testConvertCustomerCartToGuestWithEmptyQuote(): void
-    {
-        $this->checkoutSessionMock->expects($this->once())
-            ->method('getQuoteId')->willReturn(null);
-        $this->quoteRepositoryMock->expects($this->once())->method('get')->with(null)->willReturn(null);
-        $this->model->convertCustomerCartToGuest();
-    }
-
-    /**
-     * @return void
-     */
-    public function testConvertCustomerCartToGuestWithEmptyQuoteId(): void
-    {
-        $this->checkoutSessionMock->expects($this->once())
-            ->method('getQuoteId')->willReturn(1);
-        $quoteWithNoId = $this->quoteMock = $this->createMock(Quote::class);
-        $quoteWithNoId->expects($this->once())->method('getId')->willReturn(null);
-        $this->quoteRepositoryMock->expects($this->once())->method('get')->with(1)->willReturn($quoteWithNoId);
-        $this->quoteMock->expects($this->once())->method('getId')->willReturn(1);
-        $this->model->convertCustomerCartToGuest();
+        $this->model->convertCustomerCartToGuest($this->quoteMock);
     }
 
     /**
@@ -429,7 +406,7 @@ private function getExtensionAttributesMock(): MockObject
     {
         $extensionMockBuilder = $this->getMockBuilder(CartExtensionInterface::class);
         try {
-            $extensionMockBuilder->addMethods(['setShippingAssignments']);
+            $extensionMockBuilder->onlyMethods(['setShippingAssignments']);
         } catch (RuntimeException $e) {
             // do nothing as CartExtensionInterface already generated and has 'setShippingAssignments' method.
         }
diff --git a/app/code/Magento/Quote/Model/QuoteAddressValidator.php b/app/code/Magento/Quote/Model/QuoteAddressValidator.php
index 6d9a82e2d4e4b..5ac830d1b78c6 100644
--- a/app/code/Magento/Quote/Model/QuoteAddressValidator.php
+++ b/app/code/Magento/Quote/Model/QuoteAddressValidator.php
@@ -156,7 +156,7 @@ public function validateForCart(CartInterface $cart, AddressInterface $address):
         if ($cart->getCustomerIsGuest()) {
             $this->doValidateForGuestQuoteAddress($address, $cart);
         }
-        $this->doValidate($address, $cart->getCustomer()->getId());
+        $this->doValidate($address, !$cart->getCustomer()->getId() ? null : (int) $cart->getCustomer()->getId());
     }
 
     /**