Fixed runtime error if no signature is defined for group.

app/controllers/tickets_controller.rb

@@ -268,6 +268,8 @@ class TicketsController < ApplicationController
     log_view( ticket )
 
     # get signature
+    signature = {}
+    if ticket.group.signature
       signature = ticket.group.signature.attributes
 
       # replace tags
@@ -278,6 +280,7 @@ class TicketsController < ApplicationController
           :user     => current_user,
         }
       )
+    end
 
     # get related articles
     ticket = ticket.attributes