Merge pull request #11029 from inoas/patch-5

Note about allowNullableNulls

src/ORM/Rule/ExistsIn.php

@@ -56,6 +56,8 @@ class ExistsIn
      * @param object|string $repository The repository where the field will be looked for,
      * or the association name for the repository.
      * @param array $options The options that modify the rules behavior.
+     *     Options 'allowNullableNulls' will make the rule pass if given foreign keys are set to `null`.
+     *     Notice: allowNullableNulls cannot pass by database columns set to `NOT NULL`.
      */
     public function __construct($fields, $repository, array $options = [])
     {