Merge pull request #29174 from stevebauman/patch-2

[5.8] Fixed validator not failing on custom rule when message is null

src/Illuminate/Validation/Validator.php

@@ -572,7 +572,7 @@ protected function validateUsingCustomRule($attribute, $value, $rule)
         if (! $rule->passes($attribute, $value)) {
             $this->failedRules[$attribute][get_class($rule)] = [];
 
-            $messages = (array) $rule->message();
+            $messages = $rule->message() ? (array) $rule->message() : [get_class($rule)];
 
             foreach ($messages as $message) {
                 $this->messages->add($attribute, $this->makeReplacements(