Karate DSL: Convert String to Json and insert value?

Question

I need to convert an object that I receive from a java method to Json, then I need to add a value. I was trying to do this but the value is not added.

Background:
    * def jsonReport = json
    * def getDate =
  """
  function() {
    var DateTimeFormatter = Java.type('java.time.format.DateTimeFormatter');
    var dtf = DateTimeFormatter.ofPattern('uuuuMMddHHmmss');
    var ldt = java.time.LocalDateTime.now();
    return ldt.format(dtf);
  }
  """
    * def localDateTime = getDate()
    * eval if(!jsonReport.Date) jsonReport.Date = localDateTime + ''