diff --git a/src/Service/GlobalAuthenticationService.php b/src/Service/GlobalAuthenticationService.php
index 7026ff2..83e26a7 100644
--- a/src/Service/GlobalAuthenticationService.php
+++ b/src/Service/GlobalAuthenticationService.php
@@ -18,11 +18,11 @@ class GlobalAuthenticationService extends ID3BaseService
     private GlobalAuthenticationGateway $gateway;
 
     /**
-     * @var string The Profile ID to be used when verifying identities via->verifyIdentity().
+     * @var ?string The Profile ID to be used when verifying identities via->verifyIdentity().
      *
      * @see self::setProfileId()
      */
-    private string $profileId = '';
+    private ?string $profileId = null;
 
     /**
      * @var int The version of the Profile ID to be used when verifying identities via->verifyIdentity().
@@ -99,7 +99,7 @@ public function verifyIdentity(Identity $identity, ?string $customerReference =
 
         $gateway = $this->getGateway();
 
-        if (!$this->profileId) {
+        if ($this->profileId === null) {
             $error = 'An ID3global Profile ID must be set by calling setProfileId() before calling verifyIdentity().';
 
             throw new LogicException($error);
diff --git a/tests/Service/GlobalAuthenticationServiceTest.php b/tests/Service/GlobalAuthenticationServiceTest.php
index 3fc6ee9..ef1b5ee 100644
--- a/tests/Service/GlobalAuthenticationServiceTest.php
+++ b/tests/Service/GlobalAuthenticationServiceTest.php
@@ -120,7 +120,7 @@ public function fakeResponses(): array
     {
         return [
             ['profile-id', 1, 'customer-1', GlobalAuthenticationGatewayFake::IDENTITY_BAND_ALERT, 20000],
-            ['profile-id-2', 0, 'customer-2', GlobalAuthenticationGatewayFake::IDENTITY_BAND_REFER, 500],
+            ['', 0, '', GlobalAuthenticationGatewayFake::IDENTITY_BAND_REFER, 500],
         ];
     }
 }