fix(datastore): Treat head as optional to avoid errors

packages/datastore/__tests__/outbox.test.ts

@@ -90,6 +90,24 @@ describe('Outbox tests', () => {
 		});
 	});
 
+	it('Should not throw errors when Outbox.dequeue is called on an empty outbox', async () => {
+		const modelData: ModelType = JSON.parse('{}');
+		const response = {
+			...modelData,
+			_version: 1,
+			_lastChangedAt: Date.now(),
+			_deleted: false,
+		};
+
+		await Storage.runExclusive(async s => {
+			const head = await outbox.peek(s);
+
+			expect(head).toBeFalsy();
+			await expect(outbox.dequeue(s, response, TransformerMutationType.CREATE))
+				.resolves;
+		});
+	});
+
 	it('Should sync the _version from a mutation response to other items with the same `id` in the queue', async () => {
 		const last = await DataStore.query(Model, modelId);
 

packages/datastore/src/sync/outbox.ts

@@ -111,7 +111,9 @@ class MutationEventOutbox {
 			await this.syncOutboxVersionsOnDequeue(storage, record, head, recordOp!);
 		}
 
-		await storage.delete(head);
+		if (head) {
+			await storage.delete(head);
+		}
 		this.inProgressMutationEventId = undefined!;
 
 		return head;
@@ -169,7 +171,7 @@ class MutationEventOutbox {
 		head: PersistentModel,
 		recordOp: string
 	): Promise<void> {
-		if (head.operation !== recordOp) {
+		if (head?.operation !== recordOp) {
 			return;
 		}