Merge pull request #589 from pitr-ch/master

Initialize instance variables to nil, fix #566

Author: Petr Chalupa

lib/concurrent/concern/obligation.rb

@@ -138,6 +138,7 @@ def get_arguments_from(opts = {})
       # @!visibility private
       def init_obligation
         @event = Event.new
+        @value = @reason = nil
       end
 
       # @!visibility private