Fix screen xref initialization

R/Screen.R

@@ -25,6 +25,8 @@ Screen <- R6Class(
     status = NULL,
     date_started = NULL,
     date_ended = NULL,
+    xrefDB = NULL,
+    xrefID = NULL,
     #' @description Create a Screen object
     #' @param dbConnection A dbConnection object
     #' @param ID Database ID of this object
@@ -36,7 +38,8 @@ Screen <- R6Class(
     #' @param date_ended Data at which the screen was finished
     initialize = function(dbConnection = NA, ID = NA, name = NA,
                           description = NA, status = NA,
-                          date_started = NA, date_ended = NA) {
+                          date_started = NA, date_ended = NA, 
+                          xrefDB = NA, xrefID = NA) {
       if(!("DBConnection" %in% class(dbConnection))) {
         stop("DB connection object required to create Screen object")
       }