Content assistant on eclipse during play framework programming, shows "The compilation unit is not in the build path of a Java project"?

Question

package controllers;

import play.mvc.*;

import views.html.*;

/**
 * This controller contains an action to handle HTTP requests
 * to the application's home page.
 */
public class HomeController extends Controller {


    public Result index() {
        response().setCookie(
                "theme",        // name
                "blue",         // value
                3600,           // maximum age
                "",   // path
                "localhost", // domain
                false,          // secure
                true            // http only
        );
        response.
        return ok("index here");     
    }

}

Here when I press ctrl + space near response it will show a message as shown in the image below.