Doesn't work with composite_primary_keys gem

[MichaelSp]

While running user.permissions_users.each do |permission| ... I get this:

TypeError - ["user_id", "permission_id"] is not a symbol:
  bullet (4.14.4) lib/bullet/ext/object.rb:8:in `primary_key_value'
  bullet (4.14.4) lib/bullet/detector/n_plus_one_query.rb:28:in `add_possible_objects'
  bullet (4.14.4) lib/bullet/active_record42.rb:109:in `load_target'
  activerecord (4.2.0) lib/active_record/associations/collection_proxy.rb:44:in `load_target'
  activerecord (4.2.0) lib/active_record/associations/collection_proxy.rb:939:in `to_ary'
  activerecord (4.2.0) lib/active_record/relation/delegation.rb:46:in `each'

This is my permissions_user model:

class PermissionsUser < ActiveRecord::Base
  self.primary_keys = :user_id, :permission_id
  enum state: [:inherit, :no, :yes]

  belongs_to :user
  belongs_to :permission

  validates_uniqueness_of :user_id, scope: [:permission_id]
  validates_presence_of :user_id, :state, :permission_id
end