Attempting to edit the details including hardware configuration of a recently deployed virtual machine fails with the error "You must specify a password to join to a domain," or "Username and Password cannot be empty if Join Domain is selected."
This is an error with the VMware Cloud Director web control panel, which occurs when a new domain-joined virtual machine is deployed using the Cloud Director API or CloudConnect Desktop Deployment Wizard.
Discard the attempted changes, re-open the Virtual Machine Details and expand "Guest OS Customization." Clear the Guest Customization setting checkbox "Enable this VM to join to a domain," click save. After the Virtual Machine Settings are updated, try to edit the hardware configuration again.
Clearing this Checkbox does not affect the Virtual Machine's Domain Membership going forward. If it was joined to the domain upon deployment, it will retain its domain membership configuration and machine account identity in Active Directory.