How to assign placeholder text to User Field Type

I’m using a User Field type to link a Contributor (CPT) with a specific user. But in the admin area, when editing a Contributor, the meta box defaults to the first user so a user is always selected. The problem is that not all contributors have user accounts.

I’m thinking that with placeholder text in the user field (instead of the first user record), there would be no value selected by default. So when the record is saved, all is well.

Any help appreciated.

Justin

https://wordpress.org/plugins/meta-box/