Resolve #3325652

Closes #3325652

filefield_sources.module

@@ -91,11 +91,11 @@ function filefield_sources_field_widget_settings_summary_alter(&$summary, $conte
 }
 
 /**
- * Implements hook_field_widget_form_alter().
+ * Implements hook_field_widget_single_element_form_alter().
  *
  * Add file field sources widget's settings to element.
  */
-function filefield_sources_field_widget_form_alter(&$element, FormStateInterface $form_state, $context) {
+function filefield_sources_field_widget_single_element_form_alter(array &$element, FormStateInterface $form_state, array $context) {
   $plugin = $context['widget'];
   if (in_array($plugin->getPluginId(), \Drupal::moduleHandler()->invokeAll('filefield_sources_widgets'))) {
     $element['#filefield_sources_settings'] = $plugin->getThirdPartySetting('filefield_sources', 'filefield_sources');