Unable to invite customers with '&' in their email

Summary

Cannot invite customers from project (not user management) when email contains '&' character.

Steps to reproduce

1. Click on the Service Desk project > People > Customers > Invite Customers
2. Enter an email address with '&' (john&doe@example.com)
3. Click enter

Expected Results

• Email is considered valid and able to continue typing next email address or send invite

Actual Results

• Unable to invite customers

Current workaround

1. Create the user in JIRA with this email address
   Cog icon > User Management > Users > Create User
2. Remove the user from jira-users group so that he/she won't count towards the license
3. Add this user to the Service Desk Customers Role
   Projects > ServiceDeskProject > Administration > Roles