Call to a member function isEmpty() on null in date_recur_search_api_entity_build_defaults_alter

Added initial patch in MR.

We're not setting this to anything, it's just a NULL value if it's not computed becuase we're viewing the entity page. it's outside of a search api view. But we get the WSOD even though we don't have the computed field in our manage display. It throws the error regardless.

It sounds like the computed field is not correctly reporting that it's empty?

Sorry, I misread the error message.

> Call to a member function isEmpty() on null

That means that the $entity->get(FIELD) failed.

Why is the field missing? Can you debug?

Looking at $entity->get($field) on the node page gives me

Drupal\computed_field\Field\ComputedFieldClass {#2574 ▼
  #definition: 
Drupal\computed_field\Field
\
ComputedFieldDefinition {#2572 ▶}
  #name: "localgov_event_date_occurrence"
  #parent: 
Drupal\Core\Entity\Plugin\DataType
\
EntityAdapter {#2423 ▶}
  #_serviceIds: []
  #_entityStorages: []
  #stringTranslation: null
  #typedDataManager: 
Drupal\Core\TypedData
\
TypedDataManager {#594 ▶}
  #list: []
  #langcode: "en"
  #valueComputed: true
}

On the Search API page I get

Drupal\computed_field\Field\ComputedFieldClass {#9711 ▼
  #definition: 
Drupal\computed_field\Field
\
ComputedFieldDefinition {#9742 ▶}
  #name: "localgov_event_date_occurrence"
  #parent: 
Drupal\Core\Entity\Plugin\DataType
\
EntityAdapter {#9788 ▶}
  #_serviceIds: []
  #_entityStorages: []
  #stringTranslation: null
  #typedDataManager: 
Drupal\Core\TypedData
\
TypedDataManager {#1240 ▶}
  #list: array:1 [▼
    0 => 
Drupal\datetime_range\Plugin\Field\FieldType
\
DateRangeItem {#9688 ▼
      #definition: 
Drupal\Core\Field\TypedData
\
FieldItemDataDefinition {#9741 ▶}
      #name: 0
      #parent: 
Drupal\computed_field\Field
\
ComputedFieldClass {#9711}
      #_serviceIds: []
      #_entityStorages: []
      #stringTranslation: null
      #typedDataManager: 
Drupal\Core\TypedData
\
TypedDataManager {#1240 ▶}
      #values: array:3 [ …3]
      #properties: array:2 [ …2]
    }
  ]
  #langcode: "en"
  #valueComputed: true
}

I traced the NULL value to docroot/core/lib/Drupal/Core/TypedData/ComputedItemListTrait.php which the get method returns NULL if there is no value in the index.

  public function get($index) {
    if (!is_numeric($index)) {
      throw new \InvalidArgumentException('Unable to get a value with a non-numeric delta in a list.');
    }

    // Unlike the base implementation of
    // \Drupal\Core\TypedData\ListInterface::get(), we do not add an empty item
    // automatically because computed item lists need to behave like
    // non-computed ones. For example, calling isEmpty() on a computed item list
    // should return TRUE when the values were computed and the item list is
    // truly empty.
    // @see \Drupal\Core\TypedData\Plugin\DataType\ItemList::get().
    $this->ensureComputedValue();

    return $this->list[$index] ?? NULL;
  }

I think it returns NULL as the ComputeValue of src/Plugin/ComputedField/DateOccurrence.php will return an empty array. I can change this to ['now'] and the entity pages get a dateTime of the current date.

Oh. There are two get() calls and they're not the same. That's why I'm confused!

    $date_occurrence_field = $entity->get($field_name)->get(0);

$entity->get(FIELDNAME) gets us the FieldItemListInterface for the field. That one's fine, right?

FieldItemListInterface->get(0) is one of those weird magic ones maybe?

Maybe we should be calling isEmpty() on the FieldItemListInterface instead? Can you try that?

Bumping back to needs review for the updated MR.

Sorry it's taken me this long to look at this.

Reproduced the bug, confirmed the fix.

Will make a new release.

Thanks!