When attempting to switch email to an existing email, empty string error

[mattcoy-arcticleaf]

Expected behavior

When attempting to change email address of customer account to one that already exists on the store, would expect to be told the email address that already exists.

Actual behavior

Receive the following message: The email address '' is already in use by another customer. Please enter a different one.

Steps to reproduce behavior

Tested on Cornerstone Demo: https://cornerstone-light-demo.mybigcommerce.com/

1. Log in to a customer account
2. Go to the Account Settings page
3. Attempt to change email to one that is already in use on the store