Spring Boot - How to apply validators to type arguments in Kotlin?

I have the following Java class in my project

public class Post {

    public final @Nullable Optional<@Size(min = 10, max = 255) String> title;

    public Post(@JsonProperty("title") @Nullable Optional<String> title) {
        this.title = title;
    }
}

This class, when used with the @Valid annotation in a RestController, allows for null values and String values with 10 to 255 characters.

I want to replicate the same behavior in Kotlin. What I came up with was the following:

class Post(
  @JsonProperty("title") 
  val title: Optional<@Size(min = 10, max = 255) String>?
)

However, this class no longer enforces the @Size constraint and allows String values of any length.

How can I fix this and make it enforce the @Size constraint properly?