fix phpstan issues

src/Commands/EncryptCommands.php

@@ -111,8 +111,8 @@ class EncryptCommands extends DrushCommands {
    *   Validates the given encryption profile.
    * @aliases evp
    *
-   * @return array
-   *   A list of errors.
+   * @return array|null
+   *   A list of errors, if there are any errors.
    *
    * @throws \Exception
    */