Advanced Custom Fields: Extended - Fatal error: Uncaught InvalidArgumentException: item should be a Collection or an array or an object in...

Overview of the issue

You may experience a fatal error after updating the Advanced Custom Fields Multilingual plugin to version 2.1.4.1 when also using the Advanced Custom Fields: Extended and Advanced Custom Fields Pro plugins:

Fatal error: Uncaught InvalidArgumentException: item should be a Collection or an array or an object in .../wp-content/plugins/sitepress-multilingual-cms/vendor/wpml/fp/core/Obj.php:112

Workaround

Please, make sure of having a full site backup of your site before proceeding.

• Open …/wp-content/plugins/acfml/classes/class-wpml-acf-options-page.php file.
• Look for line 280.
• Replace:

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  private static function isValidOptionPagePostId( $postId ) {     return function_exists( 'acf_get_options_pages' )            && wpml_collect( acf_get_options_pages() )->first( Relation::propEq( 'post_id', $postId ) ); }

• With:

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  private static function isValidOptionPagePostId( $postId ) {     if ( function_exists( 'acf_get_options_pages' ) ) {         $optionPages = acf_get_options_pages();               if ( $optionPages ) {             return wpml_collect( acf_get_options_pages() )->first( Relation::propEq( 'post_id', $postId ) );         }           }       return false; }