Category.create NoMethodError: undefined method `nan?' for 2:Fixnum

[proton]

ruby-1.9.2-p290 :022 > Category.create
=> #<Category _id: 4eac08548524884a43000008, _type: nil, lft: 1, rgt: 2, depth: 0, parent_id: nil>
ruby-1.9.2-p290 :023 > Category.create
NoMethodError: undefined method nan?' for 2:Fixnum from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/contexts/mongo.rb:374:ingrouped'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/contexts/mongo.rb:250:in max' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/criteria.rb:43:inmax'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid_nested_set-0.1.3/lib/mongoid_nested_set/update.rb:68:in set_default_left_and_right' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:395:in_run_create_callbacks'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:81:in run_callbacks' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence/insertion.rb:25:inblock (2 levels) in prepare'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:399:in _run_save_callbacks' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:81:inrun_callbacks'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence/insertion.rb:24:in block in prepare' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence/insertion.rb:22:intap'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence/insertion.rb:22:in prepare' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence/operations/insert.rb:26:inpersist'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:44:in insert' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:149:inupsert'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:170:in block (2 levels) in create' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:170:intap'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:170:in block in create' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:273:increating'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/mongoid-2.2.3/lib/mongoid/persistence.rb:169:in create' from (irb):23 from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/railties-3.1.1/lib/rails/commands/console.rb:45:instart'
from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/railties-3.1.1/lib/rails/commands/console.rb:8:in start' from /home/proton/projects/webra/bundle/ruby/1.9.1/gems/railties-3.1.1/lib/rails/commands.rb:40:in<top (required)>'
from script/rails:7:in require' from script/rails:7:in

'ruby-1.9.2-p290 :024 >

[proton]

mongoid (2.2.3)
bson (1.4.1)

[proton]

Problem found in lib/mongoid_nested_set/update.rb:68

maxright = nested_set_scope.max(right_field_name) || 0