diff --git a/BigQuery/tests/Unit/Connection/RestTest.php b/BigQuery/tests/Unit/Connection/RestTest.php
index acbb2e117795..90432941e206 100644
--- a/BigQuery/tests/Unit/Connection/RestTest.php
+++ b/BigQuery/tests/Unit/Connection/RestTest.php
@@ -71,7 +71,7 @@ public function clientUniverseDomainConfigProvider()
             [['apiEndpoint' => 'https://foobar.com'], 'https://foobar.com/bigquery/v2/'],
             [['universeDomain' => 'googleapis.com'], 'https://bigquery.googleapis.com/bigquery/v2/'],
             [['universeDomain' => 'abc.def.ghi'], 'https://bigquery.abc.def.ghi/bigquery/v2/'],
-            [['universeDomain' => ''], '', true],
+            [['universeDomain' => null], '', true],
         ];
     }
 
diff --git a/Core/src/RestTrait.php b/Core/src/RestTrait.php
index c991c9ac734b..70966a8a0359 100644
--- a/Core/src/RestTrait.php
+++ b/Core/src/RestTrait.php
@@ -145,7 +145,7 @@ private function getApiEndpoint($default, array $config, string $apiEndpointTemp
             );
         }
 
-        if (!isset($config['universeDomain']) || empty($config['universeDomain'])) {
+        if (!isset($config['universeDomain'])) {
             throw new UnexpectedValueException(
                 'The "universeDomain" config value must be set to use the default API endpoint template.'
             );
diff --git a/Core/tests/Unit/RestTraitTest.php b/Core/tests/Unit/RestTraitTest.php
index 423aded91b5f..031a056dd85a 100644
--- a/Core/tests/Unit/RestTraitTest.php
+++ b/Core/tests/Unit/RestTraitTest.php
@@ -218,8 +218,8 @@ public function universeDomains()
             [[], '', null, true],
             [[], null, null, true],
             [['universeDomain' => null], 'ab.cd', null, true],
-            [['universeDomain' => ''], 'ab.cd', null, true],
-            [['universeDomain' => 'defg'], 'ab.cd', 'ab.cd/'],
+            [['universeDomain' => ''], 'ab.cd/', 'ab.cd/'],
+            [['universeDomain' => 'defg'], '//ab.cd//', '//ab.cd//'],
             [['universeDomain' => 'defg'], 'ab.UNIVERSE_DOMAIN.cd', 'ab.defg.cd/'],
         ];
     }
diff --git a/PubSub/tests/Unit/Connection/RestTest.php b/PubSub/tests/Unit/Connection/RestTest.php
index 0945fd9a49fa..c2cabef93cfe 100644
--- a/PubSub/tests/Unit/Connection/RestTest.php
+++ b/PubSub/tests/Unit/Connection/RestTest.php
@@ -72,7 +72,7 @@ public function clientUniverseDomainConfigProvider()
             [['apiEndpoint' => 'https://foobar.com'], 'https://foobar.com/'],
             [['universeDomain' => 'googleapis.com'], 'https://pubsub.googleapis.com/'],
             [['universeDomain' => 'abc.def.ghi'], 'https://pubsub.abc.def.ghi/'],
-            [['universeDomain' => ''], '', true],
+            [['universeDomain' => null], '', true],
         ];
     }
 
diff --git a/Storage/tests/Unit/Connection/RestTest.php b/Storage/tests/Unit/Connection/RestTest.php
index a9c8025b056b..51c97f15e099 100644
--- a/Storage/tests/Unit/Connection/RestTest.php
+++ b/Storage/tests/Unit/Connection/RestTest.php
@@ -86,7 +86,7 @@ public function clientUniverseDomainConfigProvider()
             [['apiEndpoint' => 'https://foobar.com'], 'https://foobar.com/storage/v1/'],
             [['universeDomain' => 'googleapis.com'], 'https://storage.googleapis.com/storage/v1/'],
             [['universeDomain' => 'abc.def.ghi'], 'https://storage.abc.def.ghi/storage/v1/'],
-            [['universeDomain' => ''], '', true],
+            [['universeDomain' => null], '', true],
         ];
     }