The controller threw an error when a start date was not defined because it was

trying to format the string.  In the generate method, we already have logic to
return nil if the start date is not defined, so I added a check in the fetch
method to return nil if the generate method exited with a nil status.

app/models/backlog_chart_data.rb

@@ -2,7 +2,7 @@ class BacklogChartData < ActiveRecord::Base
   unloadable
   set_table_name 'backlog_chart_data'
   belongs_to :backlog
-  
+
   def self.generate(backlog)
     # do not generate if end_date or start_date are not defined
     # or if the start date is still in the future
@@ -14,7 +14,7 @@ class BacklogChartData < ActiveRecord::Base
 
     scope = Item.sum('points', :conditions => ["items.backlog_id=? AND items.parent_id=0", backlog.id])
     done  = Item.sum('points', :include => {:issue => :status}, :conditions => ["items.parent_id=0 AND items.backlog_id=? AND issue_statuses.is_closed=?", backlog.id, true])
-    wip   = 0 
+    wip   = 0
     if data_today.nil?
       create :scope => scope, :done => done, :backlog_id => backlog.id, :created_at => Date.today.to_formatted_s(:db)
     else
@@ -25,49 +25,51 @@ class BacklogChartData < ActiveRecord::Base
     end
     data_today
   end
-  
+
   def self.fetch(options = {})
     backlog = Backlog.find(options[:backlog_id])
-    generate backlog
-    end_date = backlog.end_date || 30.days.from_now.to_date
+    if generate(backlog).nil?
+        return nil
+    end
+    end_date = backlog.end_date
     data = find_all_by_backlog_id backlog.id, :conditions => ["created_at>=? AND created_at<=?", backlog.start_date.to_formatted_s(:db), end_date.to_formatted_s(:db)], :order => "created_at ASC"
-    
+
     return nil if data.nil? || data.length==0
-    
+
     data_points = (end_date - data.first.created_at.to_date).to_i + 1
     scope = []
-    done  = [] 
+    done  = []
     days  = []
-    
+
     data.each do |d|
       scope << d.scope
       done  << d.done
       days  << d.created_at
     end
-    
+
     (1..(data_points-days.length)).to_a.each do |i|
       days << days.last + 1.day
     end
 
     scope = scope.fill(scope.last, scope.length, data_points - scope.length)
-    
+
     speed = (done.last - done.first).to_f / done.length
-    
+
     best  = [done.last]
     worst = [done.last]
-    
+
     if done.length > 1
       while best.last < scope.last && best.last > 0 && (best.length+done.length <= scope.length)
         best << (best.last + speed*1.5).round(2)
       end
       best[best.length-1] = best.last > scope.last ? scope.last : best.last
-    
+
       while worst.last < scope.last && worst.last > 0 && (worst.length+done.length <= scope.length)
         worst << (worst.last + speed*0.5).round(2)
       end
       worst[worst.length-1] = worst.last > scope.last ? scope.last : worst.last
     end
-    
+
     {
       :days    => days,
       :scope   => scope,