[Auth UI] Empty page shown after pressing Next when attempt to promote a guest user

[keithtkl]

When try to promote a guest user and the user selected email for registration, empty page will be shown if the user try to press Next with no email address inputted

• Skygear Server Date/Version: Not sure
• Application Platform: Tested on Rees

Expected Results

If the user does not input email address to register an account, should display a proper error message on the signup page

Actual Results

It redirects user to an empty page without any message for next step

Steps to reproduce

1. Install Rees and use the app with a guest account
2. Open signup page and select use email instead
3. Press Next without inputting anything on the email field