TypeError: Error #1034: 强制转换类型失败:无法将 "0.49" 转换为 mx.graphics.IFill。

TypeError: Error #1034: 强制转换类型失败:无法将 "0.49" 转换为 mx.graphics.IFill。
at mx.charts.series::LineSeries/updateDisplayList()[E:\dev\4.0.0\frameworks\projects\datavisualization\src\mx\charts\series\LineSeries.as:1091]
at mx.core::UIComponent/validateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8531]
at mx.managers::LayoutManager/validateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:663]
at mx.managers::LayoutManager/doPhasedInstantiation()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:718]
at mx.managers::LayoutManager/doPhasedInstantiationCallback()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:1072]

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx"
width="100%" height="100%" fontSize="12"
fontFamily="微软雅黑">
<s:layout>
<s:BasicLayout/>
</s:layout>
<fx:Script>
<![CDATA[
import mx.charts.ChartItem;
import mx.charts.chartClasses.Series;
import mx.charts.series.items.LineSeriesItem;
import mx.collections.ArrayCollection;
import mx.events.FlexEvent;
import mx.graphics.Stroke;

[Bindable]
//折线图数据绑定
private var lineArray:ArrayCollection = new ArrayCollection([
{seasons:"春季",rate:"0.48677"},
{seasons:"夏季",rate:"0.122343232"},
{seasons:"秋季",rate:"0.5657645"},
{seasons:"冬季",rate:"0.67484889"}
]);

/**
* 设置折线图中比率的位数
*/
public function dataFunction(series:Series, item:Object, fieldName:String):Object
{
var temp:Number = item.rate;
var number:String = formatter.format(temp);
return number;
}

public function myFillFunction(item:ChartItem, index:Number):String
{
var curItem:LineSeriesItem = LineSeriesItem(item);
var num:String = formatter.format(curItem.yNumber);
return num;
}

]]>
</fx:Script>
<fx:Declarations>
<mx:NumberFormatter id="formatter" precision="2" rounding="up"/>
</fx:Declarations>

<mx:VBox width="100%" height="100%" paddingBottom="10" paddingLeft="10" paddingRight="15"
paddingTop="10" horizontalAlign="center">
<mx:LineChart id="line" width="100%" height="90%" dataProvider="{lineArray}" showDataTips="true">
<mx:horizontalAxis>
<mx:CategoryAxis categoryField="seasons" displayName="四季"/>
</mx:horizontalAxis>

<mx:horizontalAxisRenderers>
<mx:AxisRenderer placement="bottom" tickLength="1" tickStroke="{new Stroke(0xFF0000,1)}"
axisStroke="{new Stroke(0xFF0000,1)}">
<mx:axis>
<mx:LinearAxis id="bottomAxis"/>
</mx:axis>
</mx:AxisRenderer>
</mx:horizontalAxisRenderers>

<mx:verticalAxisRenderers>
<mx:AxisRenderer placement="left" tickLength="1" tickStroke="{new Stroke(0xFF0000,1)}"
axisStroke="{new Stroke(0xFF0000,1)}">
<mx:axis>
<mx:LinearAxis id="leftAxis"/>
</mx:axis>
</mx:AxisRenderer>
</mx:verticalAxisRenderers>

<mx:series>
<mx:LineSeries verticalAxis="{leftAxis}" displayName="比率" xField="seasons" yField="rate"
fillFunction="myFillFunction"/>
</mx:series>

<mx:filters>
<fx:Array/>
</mx:filters>
</mx:LineChart>
<mx:Legend dataProvider="{line}"/>

</mx:VBox>
</s:Application>