don't confuse the due date and the last data entry date

app/models/burndown.rb

 class Burndown
-  attr_accessor :start_date, :end_date, :issues_count, :issues_weight
+  attr_accessor :start_date, :due_date, :end_date, :issues_count, :issues_weight
 
   def initialize(milestone)
     @milestone = milestone
     @start_date = @milestone.start_date
+    @due_date = @milestone.due_date
     @end_date = @milestone.due_date
     @end_date = Date.today if @end_date.present? && @end_date > Date.today
 
@@ -38,7 +39,7 @@ class Burndown
   end
 
   def valid?
-    start_date && end_date
+    start_date && due_date
   end
 
   private

app/views/shared/milestones/_burndown.html.haml

@@ -16,7 +16,7 @@
           Issues
         %button.btn.btn-xs{ data: { show: 'weight' } }
           Issue weight
-  .burndown-chart{ data: { start_date: burndown.start_date.strftime("%Y-%m-%d"), due_date: burndown.end_date.strftime("%Y-%m-%d"), chart_data: burndown.to_json } }
+  .burndown-chart{ data: { start_date: burndown.start_date.strftime("%Y-%m-%d"), due_date: burndown.due_date.strftime("%Y-%m-%d"), chart_data: burndown.to_json } }
 
 - elsif can?(current_user, :admin_milestone, @project) && cookies['hide_burndown_message'].nil?
   .burndown-hint.content-block.container-fluid