Incorect message occurs after trying to safe already existed value in unique field

[MikhailSilk]

Environment

Custom front generator version: v. 4.0.0-beta.1

Description of the bug or enhancement

Create a new project
Create a new entity
Create a new attribute with unique validation
Create a new entity management frontend component
Run the project and open the created component for edition
Create the first instance
Try to save entity instance with an existing field

AR: Incorect message occurs.

[HegelPro]

For show a correct error message need to add details about wrong fields to server error.