title: undefined method `include?' for nil:NilClass with partial validation of wizard gem
body: <p>I am trying to follow the guide for partial validation on object using the wizard gem, but I keep getting the error undefined method `include?' for nil:NilClass, cant understand what is wrong, have tried to follow the step by step instructions.</p>
  
  <p>The error in the log shows.</p>
  
  <pre><code>NoMethodError - undefined method `include?' for nil:NilClass:
  app/models/property.rb:22:in `active_or_tenants?'
  </code></pre>
  
  <p>Here is my steps controller.</p>
  
  <pre><code>class Properties::BuildController &lt; ApplicationController
    include Wicked::Wizard
  
    steps :tenant, :confirmed 
  
    def show
      @property = Property.find(params[:property_id])
      @tenants = @property.tenants.new(params[:tenant_id])
      render_wizard
    end
  
    def update
      @property = Property.find(params[:property_id])
      params[:property][:status] = step.to_s
      params[:property][:status] = 'active' if step == steps.last
      @property.update_attributes(params[:property])
      render_wizard @property
    end
  
    def create
      @property = current_user.properties.build(params[:property])
        logger.info @property.attributes
      if @property.save
          flash[:success] = "Tenant Added"
          redirect_to wizard_path(steps.second, :property_id =&gt; @property.id)
      else
          render 'edit'
      end
    end
  end
  </code></pre>
  
  <p>Property.rb</p>
  
  <pre><code>class Property &lt; ActiveRecord::Base
    attr_accessible  :name, :address_attributes, :tenants_attributes, :property_id, :status
    belongs_to :user 
  
    has_one :address, :as =&gt; :addressable
    accepts_nested_attributes_for :address, :allow_destroy =&gt; true
  
    has_many :tenants 
    accepts_nested_attributes_for :tenants, :allow_destroy =&gt; true
  
    validates :name,        :presence =&gt; true
    validates :address,     :presence =&gt; true
    validates :tenants,     :presence =&gt; true, :if =&gt; :active_or_tenants?
  
    def active?
      status == 'active'
    end
  
    def active_or_tenants?
      status.include?('tenants') || active?
    end
  end
  </code></pre>
  
  <p>Let me know if you need any other parts added to the question. Thanks in advance.</p>