-fix error message accessing object

[nicolas-san]

I use the last values of the ticket object instead of search for the last of the messages persistent collection

#lastUser: 1
  #lastUserObject: BaseUser {#121}
  #lastMessage: DateTime {#1315
    +"date": "2017-05-12 11:40:00.000000"
    +"timezone_type": 3
    +"timezone": "Europe/Berlin"
  }

Can you review if it's ok for you, and if this code do the same as you have done ?