diff --git a/app/models/grader_process.rb b/app/models/grader_process.rb
--- a/app/models/grader_process.rb
+++ b/app/models/grader_process.rb
@@ -32,7 +32,11 @@
   
   def report_active(task=nil)
     self.active = true
-    self.task_id = task.id
+    if task!=nil
+      self.task_id = task.id
+    else
+      self.task_id = nil
+    end
     self.task_type = task.class.to_s
     self.save
   end