fix(core): Prevent workflow history saving error from happening (#7812)

When performing actions such as renaming a workflow or updating its
settings, n8n errors with "Failed to save workflow version" in the
console although the saving process was successful. We are now correctly
checking whether `nodes` and `connections` exist and only then save a
snapshot.

Github issue / Community forum post (link here to close automatically):

packages/cli/test/unit/shared/mockObjects.ts

@@ -0,0 +1,42 @@
+import { User } from '@db/entities/User';
+import { Role } from '@db/entities/Role';
+import { CredentialsEntity } from '@db/entities/CredentialsEntity';
+
+import {
+	randomCredentialPayload,
+	randomEmail,
+	randomInteger,
+	randomName,
+} from '../../integration/shared/random';
+
+export const wfOwnerRole = () =>
+	Object.assign(new Role(), {
+		scope: 'workflow',
+		name: 'owner',
+		id: randomInteger(),
+	});
+
+export const mockCredRole = (name: 'owner' | 'editor'): Role =>
+	Object.assign(new Role(), {
+		scope: 'credentials',
+		name,
+		id: randomInteger(),
+	});
+
+export const mockCredential = (): CredentialsEntity =>
+	Object.assign(new CredentialsEntity(), randomCredentialPayload());
+
+export const mockUser = (): User =>
+	Object.assign(new User(), {
+		id: randomInteger(),
+		email: randomEmail(),
+		firstName: randomName(),
+		lastName: randomName(),
+	});
+
+export const mockInstanceOwnerRole = () =>
+	Object.assign(new Role(), {
+		scope: 'global',
+		name: 'owner',
+		id: randomInteger(),
+	});