Simplified the submoduleDirectories

__test__/git-auth-helper.test.ts

@@ -813,7 +813,7 @@ async function setup(testName: string): Promise<void> {
     lfs: false,
     submodules: false,
     nestedSubmodules: false,
-    submoduleDirectories: null,
+    submoduleDirectories: [],
     persistCredentials: true,
     ref: 'refs/heads/main',
     repositoryName: 'my-repo',

__test__/input-helper.test.ts

@@ -94,7 +94,7 @@ describe('input-helper tests', () => {
     expect(settings.showProgress).toBe(true)
     expect(settings.lfs).toBe(false)
     expect(settings.ref).toBe('refs/heads/some-ref')
-    expect(settings.submoduleDirectories).toBe(null)
+    expect(settings.submoduleDirectories).toStrictEqual([])
     expect(settings.repositoryName).toBe('some-repo')
     expect(settings.repositoryOwner).toBe('some-owner')
     expect(settings.repositoryPath).toBe(gitHubWorkspace)