Ruby on Rails

I have the following error:

ERROR["test_character_should_be_valid", CharacterTest, 0.214787]  test_character_should_be_valid#CharacterTest (0.21s)  NoMethodError:         NoMethodError: undefined method `val' for "$1":Arel::Nodes::BindParam  app/models/user.rb:11:in `block in <class:User>'  test/models/character_test.rb:8:in `setup'

From the following test: test/models/character_test.rb:

    require 'test_helper'        class CharacterTest < ActiveSupport::TestCase          def setup          @user = User.new(name: "Example User", email: "user@example.com", callsign: "example",                           password: "foobar", password_confirmation: "foobar")          @user.save          @character = @user.character        end          test "character should be valid" do          assert @character.valid?        end        end # CharacterTest

In the gemfile:

gem 'arel', '6.0.0.beta2'

character.rb:

class Character < ActiveRecord::Base    belongs_to :sociable, polymorphic: true  end

user.rb:

class User < ActiveRecord::Base      has_one  :character, as: :sociable      before_validation do      self.create_character unless character    end    .    .  end

I can't find anything about this particular arel error. My arel gem is 6.0.0.beta2, which seems to fix other problems (as in here). Has anyone seen anything like this before?