fix: exception message

Co-authored-by: MGatner <[email protected]>

Author: kenjis

system/Helpers/Array/ArrayHelper.php

@@ -130,7 +130,7 @@ public static function dotKeyExists(string $index, array $array): bool
     {
         if (str_ends_with($index, '*') || str_contains($index, '*.*')) {
             throw new InvalidArgumentException(
-                'You must set key right after "*". Invalid index: "' . $index . '"'
+                'You must set a key right after "*". Invalid index: "' . $index . '"'
             );
         }