diff --git a/README.md b/README.md
index d376c49..75200a3 100644
--- a/README.md
+++ b/README.md
@@ -116,7 +116,7 @@ Please refer to the [release page](https://github.com/actions/checkout/releases/
     # Default: false
     submodules: ''
 
-    # A list of submodules to use when `submodules` is `true`.
+    # A list of submodules to checkout.
     # Default: null
     submodule-directories: ''
 
diff --git a/__test__/git-auth-helper.test.ts b/__test__/git-auth-helper.test.ts
index ff60bae..6666dca 100644
--- a/__test__/git-auth-helper.test.ts
+++ b/__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',
diff --git a/__test__/input-helper.test.ts b/__test__/input-helper.test.ts
index 35c1848..75eb546 100644
--- a/__test__/input-helper.test.ts
+++ b/__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)
diff --git a/action.yml b/action.yml
index d18a526..e930462 100644
--- a/action.yml
+++ b/action.yml
@@ -94,7 +94,7 @@ inputs:
     default: false
   submodule-directories:
     description: >
-      A list of submodules to use when `submodules` is `true`.
+      A list of submodules to checkout.
     default: null
   set-safe-directory:
     description: Add repository path as safe.directory for Git global config by running `git config --global --add safe.directory <path>`
diff --git a/dist/index.js b/dist/index.js
index aba7b84..abd0a75 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -797,30 +797,15 @@ class GitCommandManager {
     }
     submoduleUpdate(fetchDepth, recursive, submoduleDirectories) {
         return __awaiter(this, void 0, void 0, function* () {
-            if (submoduleDirectories) {
-                for (const submodule of submoduleDirectories) {
-                    const args = ['-c', 'protocol.version=2'];
-                    args.push('submodule', 'update', '--init', '--force', submodule);
-                    if (fetchDepth > 0) {
-                        args.push(`--depth=${fetchDepth}`);
-                    }
-                    if (recursive) {
-                        args.push('--recursive');
-                    }
-                    yield this.execGit(args);
-                }
+            const args = ['-c', 'protocol.version=2'];
+            args.push('submodule', 'update', '--init', '--force', ...submoduleDirectories);
+            if (fetchDepth > 0) {
+                args.push(`--depth=${fetchDepth}`);
             }
-            else {
-                const args = ['-c', 'protocol.version=2'];
-                args.push('submodule', 'update', '--init', '--force');
-                if (fetchDepth > 0) {
-                    args.push(`--depth=${fetchDepth}`);
-                }
-                if (recursive) {
-                    args.push('--recursive');
-                }
-                yield this.execGit(args);
+            if (recursive) {
+                args.push('--recursive');
             }
+            yield this.execGit(args);
         });
     }
     submoduleStatus() {
@@ -1820,7 +1805,7 @@ function getInputs() {
         // Submodules
         result.submodules = false;
         result.nestedSubmodules = false;
-        result.submoduleDirectories = null;
+        result.submoduleDirectories = [];
         const submodulesString = (core.getInput('submodules') || '').toUpperCase();
         if (submodulesString == 'RECURSIVE') {
             result.submodules = true;
@@ -1835,9 +1820,6 @@ function getInputs() {
             if (!result.submodules)
                 result.submodules = true;
         }
-        else {
-            result.submoduleDirectories = null;
-        }
         core.debug(`submodules = ${result.submodules}`);
         core.debug(`recursive submodules = ${result.nestedSubmodules}`);
         core.debug(`submodule directories = ${result.submoduleDirectories}`);
diff --git a/src/git-command-manager.ts b/src/git-command-manager.ts
index 9c37043..bc73118 100644
--- a/src/git-command-manager.ts
+++ b/src/git-command-manager.ts
@@ -57,7 +57,7 @@ export interface IGitCommandManager {
   submoduleUpdate(
     fetchDepth: number,
     recursive: boolean,
-    submoduleDirectories: string[] | null
+    submoduleDirectories: string[]
   ): Promise<void>
   submoduleStatus(): Promise<boolean>
   tagExists(pattern: string): Promise<boolean>
@@ -416,35 +416,25 @@ class GitCommandManager {
   async submoduleUpdate(
     fetchDepth: number,
     recursive: boolean,
-    submoduleDirectories: string[] | null
+    submoduleDirectories: string[]
   ): Promise<void> {
-    if (submoduleDirectories) {
-      for (const submodule of submoduleDirectories) {
-        const args = ['-c', 'protocol.version=2']
-        args.push('submodule', 'update', '--init', '--force', submodule)
-        if (fetchDepth > 0) {
-          args.push(`--depth=${fetchDepth}`)
-        }
-
-        if (recursive) {
-          args.push('--recursive')
-        }
-
-        await this.execGit(args)
-      }
-    } else {
-      const args = ['-c', 'protocol.version=2']
-      args.push('submodule', 'update', '--init', '--force')
-      if (fetchDepth > 0) {
-        args.push(`--depth=${fetchDepth}`)
-      }
-
-      if (recursive) {
-        args.push('--recursive')
-      }
-
-      await this.execGit(args)
+    const args = ['-c', 'protocol.version=2']
+    args.push(
+      'submodule',
+      'update',
+      '--init',
+      '--force',
+      ...submoduleDirectories
+    )
+    if (fetchDepth > 0) {
+      args.push(`--depth=${fetchDepth}`)
     }
+
+    if (recursive) {
+      args.push('--recursive')
+    }
+
+    await this.execGit(args)
   }
 
   async submoduleStatus(): Promise<boolean> {
diff --git a/src/git-source-settings.ts b/src/git-source-settings.ts
index 1555489..518e0bf 100644
--- a/src/git-source-settings.ts
+++ b/src/git-source-settings.ts
@@ -77,7 +77,7 @@ export interface IGitSourceSettings {
   /**
    * Indicates which submodule paths to checkout
    */
-  submoduleDirectories: string[] | null
+  submoduleDirectories: string[]
 
   /**
    * The auth token to use when fetching the repository
diff --git a/src/input-helper.ts b/src/input-helper.ts
index f367ce0..5b2ff6c 100644
--- a/src/input-helper.ts
+++ b/src/input-helper.ts
@@ -125,7 +125,7 @@ export async function getInputs(): Promise<IGitSourceSettings> {
   // Submodules
   result.submodules = false
   result.nestedSubmodules = false
-  result.submoduleDirectories = null
+  result.submoduleDirectories = []
   const submodulesString = (core.getInput('submodules') || '').toUpperCase()
   if (submodulesString == 'RECURSIVE') {
     result.submodules = true
@@ -138,8 +138,6 @@ export async function getInputs(): Promise<IGitSourceSettings> {
   if (submoduleDirectories.length > 0) {
     result.submoduleDirectories = submoduleDirectories
     if (!result.submodules) result.submodules = true
-  } else {
-    result.submoduleDirectories = null
   }
 
   core.debug(`submodules = ${result.submodules}`)