def sql_for_tt_booking_issue_field(field, operator, value)
    sql = "( #{Issue.table_name}.id #{operator == "=" ? 'IN' : 'NOT IN'} (" + value.collect { |val| "'#{self.class.connection.quote_string(val)}'" }.join(",") + ") "
    if operator == "!"
      sql << " OR #{Issue.table_name}.id IS NULL)"
    else