diff --git a/src/Fortress/Validator/CustomValidatorRules.php b/src/Fortress/Validator/CustomValidatorRules.php
index a13276b..699f839 100644
--- a/src/Fortress/Validator/CustomValidatorRules.php
+++ b/src/Fortress/Validator/CustomValidatorRules.php
@@ -94,6 +94,6 @@ public static function validatePhoneUS(string $field, mixed $value): bool
      */
     public static function validateUsername(string $field, mixed $value): bool
     {
-        return preg_match('/^([a-z0-9\.\-_])+$/i', $value) === 1;
+        return preg_match('/^([a-z0-9\.\-_])+$/i', strval($value)) === 1;
     }
 }
diff --git a/tests/Fortress/Validator/ServerSideValidatorTest.php b/tests/Fortress/Validator/ServerSideValidatorTest.php
index d28e662..758de6f 100644
--- a/tests/Fortress/Validator/ServerSideValidatorTest.php
+++ b/tests/Fortress/Validator/ServerSideValidatorTest.php
@@ -814,6 +814,9 @@ public function testValidateUsername(): void
             'user_name' => '',
         ]));
 
+        // Check with missing data
+        $this->assertEmpty($this->validator->validate($schema, []));
+
         // Check failing validations - Code not allowed
         $errors = $this->validator->validate($schema, [
             'user_name' => "<script>alert('I got you');</script>",
@@ -836,6 +839,33 @@ public function testValidateUsername(): void
         $this->assertSame(["Sorry buddy, that's not a valid username."], $errors['user_name']);
     }
 
+    /**
+     * Test specific bug: When required validator rule is defined, username
+     * validator is still called, even if there's no data. This is not the case
+     * without "required". In this case, `validateUsername` should be ignored,
+     * or accept a null value.
+     */
+    public function testValidateUsernameForMissingData(): void
+    {
+        // Arrange
+        $schema = new RequestSchema([
+            'user_name' => [
+                'validators' => [
+                    'required' => [
+                        'message' => 'Username required',
+                    ],
+                    'username' => [
+                        'message' => "Sorry buddy, that's not a valid username.",
+                    ],
+                ],
+            ],
+        ]);
+
+        $errors = $this->validator->validate($schema, []);
+        $this->assertNotEmpty($errors);
+        $this->assertSame(['Username required', "Sorry buddy, that's not a valid username."], $errors['user_name']);
+    }
+
     public function testDomainRulesClientOnly(): void
     {
         // Arrange