diff --git a/tests/Unit/Pdk/Context/Service/WcContextServiceTest.php b/tests/Unit/Pdk/Context/Service/WcContextServiceTest.php
index ae2e6194f..6892bc3b7 100644
--- a/tests/Unit/Pdk/Context/Service/WcContextServiceTest.php
+++ b/tests/Unit/Pdk/Context/Service/WcContextServiceTest.php
@@ -98,7 +98,7 @@ function add_product_to_cart(?int $shippingClassId = null)
         ],
         'expected' => [
             'basePrice'            => 0.0,
-            'highestShippingClass' => null,
+            'highestShippingClass' => '',
         ],
     ],
     'flat rate with price'           => [
@@ -109,7 +109,7 @@ function add_product_to_cart(?int $shippingClassId = null)
         ],
         'expected' => [
             'basePrice'            => 0.0,
-            'highestShippingClass' => null,
+            'highestShippingClass' => '',
         ],
     ],
     'product without shipping class' => [
@@ -118,7 +118,7 @@ function add_product_to_cart(?int $shippingClassId = null)
         ],
         'expected' => [
             'basePrice'            => 0.0,
-            'highestShippingClass' => null,
+            'highestShippingClass' => '',
         ],
     ],
     'flat rate without price'        => [
@@ -128,7 +128,7 @@ function add_product_to_cart(?int $shippingClassId = null)
         ],
         'expected' => [
             'basePrice'            => 0.0,
-            'highestShippingClass' => null,
+            'highestShippingClass' => '',
         ],
     ],
     'term as array'                  => [
@@ -139,7 +139,7 @@ function add_product_to_cart(?int $shippingClassId = null)
         ],
         'expected' => [
             'basePrice'            => 0.0,
-            'highestShippingClass' => null,
+            'highestShippingClass' => '',
         ],
     ],
 ]);