Fix linter errors

frontend/app/components/auth/__email-login-form/auth__email-login-form.test.tsx

@@ -26,7 +26,7 @@ function simulateInput(input: ReactWrapper, value: string) {
 
 describe('EmailLoginForm', () => {
   const testUser = ({} as any) as User;
-  const onSuccess = jest.fn(async () => {});
+  const onSuccess = jest.fn(async () => undefined);
   const onSignIn = jest.fn(async () => testUser);
 
   beforeEach(() => {

frontend/app/components/comment-form/text-expander.tsx

@@ -88,7 +88,7 @@ export const TextExpander: FunctionalComponent = ({ children }) => {
         expander.removeEventListener('text-expander-value', textExpanderValueListener);
       };
     }
-    return () => {};
+    return () => undefined;
   }, [theme]);
   if (StaticStore.config.emoji_enabled) {
     return <text-expander ref={expanderRef}>{children}</text-expander>;

frontend/app/components/comment/comment.test.tsx

@@ -146,7 +146,7 @@ describe('<Comment />', () => {
     });
 
     it('disabled for already upvoted comment', async () => {
-      const voteSpy = jest.fn(async () => {});
+      const voteSpy = jest.fn(async () => undefined);
       const element = mount(
         <Comment
           {...(DefaultProps as Props)}
@@ -180,7 +180,7 @@ describe('<Comment />', () => {
     }, 30000);
 
     it('disabled for already downvoted comment', async () => {
-      const voteSpy = jest.fn(async () => {});
+      const voteSpy = jest.fn(async () => undefined);
       const element = mount(
         <Comment
           {...(DefaultProps as Props)}

frontend/app/store/user/reducers.test.ts

@@ -70,12 +70,12 @@ describe('user', () => {
     );
     const dispatch = jest.fn();
     const getState = jest.fn();
-    await logIn({ name: 'google' })(dispatch, getState, undefined).catch(() => {});
+    await logIn({ name: 'google' })(dispatch, getState, undefined).catch(() => undefined);
     expect(dispatch).not.toBeCalled();
   });
 
   it('should unset user on logOut', async () => {
-    (api.logOut as any).mockImplementation(async (): Promise<void> => {});
+    (api.logOut as any).mockImplementation(async (): Promise<void> => undefined);
     const dispatch = jest.fn();
     const getState = jest.fn();
     await logout()(dispatch, getState, undefined);