### What?
When duplicating a document with `unique` fields, we append `- Copy` to
the field value.
The issue is that this is happening when the field is empty resulting in
values being added that look like: `undefined - Copy` or `null - Copy`.
### Why?
We are not checking the incoming value in all cases.
### How?
Checks the value exists, is a string, and is not just an empty space
before appending `- Copy`.
At first glance it looks incorrect to return required fields with
`undefined` - however when duplicating a document, the new document is
always created as a `draft` so it is not an issue to return `undefined`.
Closes#11373
74996fd511