问为什么Rails在我的表格中如果是空白，为什么不识别为零呢？

EN

    NULL_ATTRS = %w( start_masterlocation_id )
    before_save :nil_if_blank

    protected

    def nil_if_blank
    NULL_ATTRS.each { |attr| self[attr] = nil if self[attr].blank? }
    end

    <%= hidden_field :newsavedmap, :start_masterlocation_id, :id => "start-masterlocation-id-field" %>

    def maptry
    @itinerary = Itinerary.find(params[:id])
    if @itinerary.user_id == current_user.id
    respond_to do |format|
    @masterlocation = Masterlocation.find(:all)
    format.html do
    end
    format.xml  { render :xml => @masterlocation }
    format.js do
    @masterlocation = Masterlocation.find(:all)
    render :json => @masterlocation.to_json(:only => [:id, :nickname, :latitude, :longitude])
    end
    end
    if params[:newsavedmap_id]
    @newsavedmap = Newsavedmap.find(:first, :conditions => {:id => params[:newsavedmap_id]})
    @waypoint = Waypoint.find(:all, :conditions => {:newsavedmap_id => params[:newsavedmap_id]})
    @newsavedmap.id = params[:newsavedmap_id]
    @newsavedmap.mapname = Newsavedmap.find(:first, :conditions => {:id => params[:newsavedmap_id]}).mapname
    @newsavedmap.optimize = Newsavedmap.find(:first, :conditions => {:id => params[:newsavedmap_id]}).optimize
    if !@newsavedmap.start_masterlocation_id.nil?       
    @start_name = Masterlocation.find(:first, :conditions => {:id => @newsavedmap.start_masterlocation_id}).name
    end
    if !@newsavedmap.end_masterlocation_id.nil?     
    @end_name = Masterlocation.find(:first, :conditions => {:id => @newsavedmap.end_masterlocation_id}).name
    end
    else
    @newsavedmap = Newsavedmap.new  
    end
    else
    redirect_to '/'
    end
    end

    undefined method `name' for nil:NilClass