         gquery_key: "merit_order_#{k}_operating_costs_in_merit_order_table"
       D3.merit_order.series.push @gquery_y
 
-    value_x: => @gquery_x.future_value() || 0
+    value_x: => @gquery_x.safe_future_value()
+
     value_y: =>
       if @get('key') == 'must_run'
         1
       else
         @original_y_value()
 
-    original_y_value: => @gquery_y.future_value() || 0
+    original_y_value: => @gquery_y.safe_future_value()
 
     label: => @get('label') || @get('key')
 

      @series_height = 280
      @x = d3.scale.linear().domain([0, 100]).range([0, @width])
      @y = d3.scale.linear().domain([0, 100]).range([0, @series_height])
      # inverted scale used by the y-axis
      @yAxisScale = d3.scale.linear().domain([0, 100]).range([@series_height, 0])
      @xAxis = d3.svg.axis().scale(@x).ticks(4).orient("bottom")
      @yAxis = d3.svg.axis().scale(@yAxisScale).ticks(4).orient("left")
      @svg = d3.select("#d3_container_merit_order").
        append("svg:svg").
        attr("height", @height + margins.top + margins.bottom).
        attr("width", @width + margins.left + margins.right).
        append("svg:g").
        attr("transform", "translate(#{margins.left}, #{margins.top})")

      # axis
      @svg.append("svg:g").
        attr("class", "x_axis").
        attr("transform", "translate(0, #{@height})").
        call(@xAxis)
      @svg.append("svg:g").
        attr("class", "y_axis").
        call(@yAxis)
      @svg.append("svg:text").
        text('Operating Costs [EUR/MWh]').
        attr("x", @height / -2).
        attr("y", -25).
        attr("text-anchor", "middle").
        attr("class", "axis_label").
        attr("transform", "rotate(270)")

      @svg.append("svg:text")
        .text('Installed Capacity [MW]')

        left_margin: 15

    refresh: =>
      max_height = @nodes.max_height()
      @y.domain([0, max_height])
      @inverted_y.domain([0, max_height])
      @x.domain([0, @nodes.total_width()])
      @svg.selectAll(".x_axis").transition().call(@x_axis.scale(@x))
      @svg.selectAll(".y_axis").transition().call(@y_axis.scale(@inverted_y))

      @min_node_height = 2

