ruby on rails - nil is not a symbol accepts_nested_attributes_for has_one association -

i trying accepts_nested_attributes_for working has_one association. have following set using mongoid.

class foo   include mongoid::document   include mongoid::timestamps   include mongoid::paranoia    has_and_belongs_to_many :bars, inverse_of: nil end  class bar   include mongoid::document   include mongoid::paranoia    has_one :magazine, class_name: 'foo', dependent: :destroy, inverse_of: nil   accepts_nested_attributes_for :magazine end 

when following in rails console seem following output.

r = bar.new => #<bar _id: 1213 ....  [2] pry(main)> r.foo.build typeerror: nil not symbol /users/home/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems /mongoid-3.1.6/lib/mongoid/attributes.rb:155:in `respond_to? 

this blog post writeup of inverse_of. instead of inverse_of: nil in models, have specify symbol. example, :bars association should declared inverse_of: :magazine.