To reproduce:
Go to Basic custom block type fields management and try to add an entityreference field...
Notice: Undefined index: type in Drupal\Core\TypedData\TypedDataManager->create() (line 131 of core/lib/Drupal/Core/TypedData/TypedDataManager.php).
InvalidArgumentException: Invalid data type <em class="placeholder"></em> has been given. in Drupal\Core\TypedData\TypedDataFactory->createInstance() (line 44 of /var/www/d8/core/lib/Drupal/Core/TypedData/TypedDataFactory.php).Somehow in the $definition passed in TypedDataManager::create() there are only the field settings:/