Fatal error: __clone method called on non-object

Hi @sinn, great work! Just fixed patch paths.

Since NULL is a valid return value for getEntity, adding a check for it sounds good.

+++ b/core/modules/views/src/Plugin/views/field/Field.php
@@ -806,7 +806,13 @@ public function getItems(ResultRow $values) {
+      if (is_object($original_entity))  {

getEntity either returns an object implementing \Drupal\Core\Entity\EntityInterface or null, so i'd just do if ($original_entity) { , either way you know you are dealing with one or the other.

Also, this needs tests.

+++ b/core/modules/views/src/Plugin/views/field/Field.php
@@ -806,7 +806,13 @@ public function getItems(ResultRow $values) {
+      $original_entity = $this->getEntity($values);
+      if (is_object($original_entity))  {
+        $entity = $this->createEntityForGroupBy($original_entity, $values);
+      }
+      else {
+        $entity = NULL;
+      }

According to the documentation of getEntity we return EntityInterface|null, so we could simplify this a bit more here: if ($entity = $this->getEntity($values)) { $entity = $this-> ... and skip the else completely.

based on dawehner comments, trying another patch.

I think this is obsolete for 8.3.x as following code is used in Drupal\views\Plugin\views\field\EntityField (successor of Drupal\views\Plugin\views\field\Field):

      // Optional relationships may not provide an entity at all. So we can't
      // use createEntityForGroupBy() for those rows.
      if ($entity = $this->getEntity($values)) {
        $entity = $this->createEntityForGroupBy($entity, $values);
        // Some bundles might not have a specific field, in which case the faked
        // entity doesn't have it either.
        $build_list = isset($entity->{$this->definition['field_name']}) ? $entity->{$this->definition['field_name']}->view($display) : NULL;
      }
      else {
        $build_list = NULL;
      }

Yup, fixed in #2666166: View with not required relationship and aggregation enabled fails to execute. You guys should get credit in that issue.