Forum: Rails deployment please help(writing conditions using haml)

in ma project there is a model named campaigns and delivery_schedules .
in  delivery_schedules i defined a method called below

def get_scheduled_time

  self.delivery_date.to_s << " " << self.delivery_hour.to_s << ":" <<
self.delivery_minute.to_s << " " << self.delivery_meridiem.upcase
 end
 in ma view page i write code lik this to print those values like this
below

%dt
    %b #{t :delivery_status}:
  = t(campaign.delivery_status,:On_Date,:time_spec
=>campaign.delivery_schedule.get_scheduled_time())

but i am gettting  errors lik this

 Showing app/views/campaigns/_metrics.html.haml where line #19 raised:

You have a nil object when you didn't expect it!
The error occurred while evaluating nil.delivery_schedule

also in a yml  file  i  defined  some parameters lik this

 delivery_status: Delivery Status
  on: on
  On_Date: "On {{time_spec}}"
this is the result i am  expecting

Scheduled On Mar 30, 2011 07:00 ( Scheduled On{{ value}}

can anyone pls  help me or giv me idea   to  solve it