“message” field is empty in error response Spring Boot

Ok got it, they have changed the default value for server.error.include-message to “never” (see the comment section here: Spring 2.3.0 Release Info

All the default values are listed here:
Spring Boot Reference Documentation

Just configure your application.yaml (or properties) like this.

server:
  error:
    include-message: always
    include-binding-errors: always

Mind that showing error messages may leak information about your server implementation.