Add check for data object when getting document dependencies

src/DataObject/DataObjectDocument.php

@@ -404,8 +404,17 @@ public function getDependentDocuments(): array
             return is_subclass_of($class, DataObject::class);
         });
         $ownedDataObject = $this->getDataObject();
+
         $docs = [];
 
+        // make sure we have a data object
+        // if not (it might have been deleted), then return empty dependency
+        // documents with the assumption that if there are any dependencies
+        // they will be handled separately
+        if (!$ownedDataObject) {
+            return $docs;
+        }
+
         foreach ($dataObjectClasses as $class) {
             // Start with a singleton to look at the model first, then get real records if needed
             $owningDataObject = Injector::inst()->get($class);