@hardik, Comment there in code itself explain that we had converted from arra...

@hardik, Comment there in code itself explain that we had converted from array to string as "The possibility to pass an array as source value to the plugin will be removed in drupal:9.0.0. Pass a string value instead." So we don't have to remove entire code. As test case failed due to removing of reset() from your patch as $value is array.