Merge branch 'fix-repo-settings-file-upload-error' into 'master'

Fix bug causing repository mirror settings UI to break

Closes #55134

See merge request gitlab-org/gitlab-ce!23712

app/assets/javascripts/lib/utils/file_upload.js

 export default (buttonSelector, fileSelector) => {
   const btn = document.querySelector(buttonSelector);
   const fileInput = document.querySelector(fileSelector);
+
+  if (!btn || !fileInput) return;
+
   const form = btn.closest('form');
 
   btn.addEventListener('click', () => {

changelogs/unreleased/fix-repo-settings-file-upload-error.yml

+---
+title: Fix bug causing repository mirror settings UI to break
+merge_request: 23712
+author:
+type: fixed

spec/javascripts/lib/utils/file_upload_spec.js

@@ -9,7 +9,10 @@ describe('File upload', () => {
         <span class="js-filename"></span>
       </form>
     `);
+  });
 
+  describe('when there is a matching button and input', () => {
+    beforeEach(() => {
       fileUpload('.js-button', '.js-input');
     });
 
@@ -33,4 +36,29 @@ describe('File upload', () => {
 
       expect(document.querySelector('.js-filename').textContent).toEqual('index.js');
     });
+  });
+
+  it('fails gracefully when there is no matching button', () => {
+    const input = document.querySelector('.js-input');
+    const btn = document.querySelector('.js-button');
+    fileUpload('.js-not-button', '.js-input');
+
+    spyOn(input, 'click');
+
+    btn.click();
+
+    expect(input.click).not.toHaveBeenCalled();
+  });
+
+  it('fails gracefully when there is no matching input', () => {
+    const input = document.querySelector('.js-input');
+    const btn = document.querySelector('.js-button');
+    fileUpload('.js-button', '.js-not-input');
+
+    spyOn(input, 'click');
+
+    btn.click();
+
+    expect(input.click).not.toHaveBeenCalled();
+  });
 });