private function createNewCollection($relationship) { if ($relationship instanceof FieldRelationship) { if ($relationship->isMultiple) { if ($relationship->isPolymorphic) { $this->relatedViaFieldOnEntity[$relationship->relationshipName] = PolymorphicCollection::forge(null); } else { $this->relatedViaFieldOnEntity[$relationship->relationshipName] = Collection::forge($relationship->modelType); } } else { throw new InvalidTypeException('Single Field Relationships do not require a collection'); } } else { if ($relationship instanceof ReferencedRelationship) { $this->relatedViaFieldOnExternalEntity[$relationship->relationshipName] = Collection::forge($relationship->modelType); } } }