Warning : foreach() argument must be of type array|object, null given dans inline_entity_form_close_all_forms()

inline_entity_form.module line 288

On close, getting that warning + Oops, something went wrong. Check your browser's developer console for more details.

Simply changing line 287 with this would probably be enough

$entities = $form_state->get(['inline_entity_form', $ief_id, 'entities']) ?? [];