Removed entity reference using Conditional Field causes Warning: array_diff_key():

Same here, in my case the form submission was also creating an empty child entity.

Don't know if it's too hackish, but just checking if drupal_array_get_nested_value() returns something before calling the $controller->entityFormSubmit() did the trick for me. Apparently everything OK now.

Patch attached

Looks like you uploaded the wrong patch.

sorry!
attached the correct one

I had a very similar scenario.
My scenario:
I have multiple entity references using Inline Entity Forms under People -> Accounts.
I use conditional fields to display only the entity references selected by the user

When I submit the form, I get the same error listed above:
Warning: array_diff_key(): Argument #1 is not an array in EntityInlineEntityFormController->entityFormSubmit() (line 307 of sites/all/modules/inline_entity_form/includes/entity.inline_entity_form.inc).
Warning: Invalid argument supplied for foreach() in EntityInlineEntityFormController->entityFormSubmit() (line 308 of sites/all/modules/inline_entity_form/includes/entity.inline_entity_form.inc)

Applying the patch successfully remove the errors on my site.

I have a similar problem as #1. I have a entity reference field that is hidden using conditional fields when a particular value is selected in a dropdown list. The reference field is a single value field and not required. When I save the host node without filling in any of the child node fields, an empty child node is saved.

I applied the patch from #7 to the latest version "7.x-1.6" but I still get these empty childs being saved.

The 4 year old patch in #7 to inline_entity_form.module does not apply to the latest inline_entity_form 7.x-1.x-dev and if still applicable needs a reroll.

Checking patch inline_entity_form.module...
error: while searching for:
 *   The form state of the parent form.
 */
function inline_entity_form_entity_form_submit($entity_form, &$form_state) {
  $ief_id = $entity_form['#ief_id'];
  $instance = $form_state['inline_entity_form'][$ief_id]['instance'];
  // Instantiate the controller and validate the form.
  $controller = inline_entity_form_get_controller($instance);
  $controller->entityFormSubmit($entity_form, $form_state);
  inline_entity_form_cleanup_entity_form_state($entity_form, $form_state);

  if ($entity_form['#op'] == 'add') {
    // Determine the correct weight of the new element.
    $weight = 0;
    if (!empty($form_state['inline_entity_form'][$ief_id]['entities'])) {
      $weight = max(array_keys($form_state['inline_entity_form'][$ief_id]['entities'])) + 1;
    }
    // Add the entity to form state, mark it for saving, and close the form.
    $form_state['inline_entity_form'][$ief_id]['entities'][] = array(
      'entity' => $entity_form['#entity'],
      'weight' => $weight,
      'form' => NULL,
      'needs_save' => TRUE,
    );
  }
  else {
    $delta = $entity_form['#ief_row_delta'];
    $form_state['inline_entity_form'][$ief_id]['entities'][$delta]['entity'] = $entity_form['#entity'];
    $form_state['inline_entity_form'][$ief_id]['entities'][$delta]['needs_save'] = TRUE;
  }
}


error: patch failed: inline_entity_form.module:967
error: inline_entity_form.module: patch does not apply