Errors randomly in my custom tooltip

Question

Im getting these errors randomly in my custom tooltip:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at mx.managers::ToolTipManagerImpl/http://www.adobe.com/2006/flex/mx/internal::positionTip()[E:\dev\4.x\frameworks\projects\f ramework\src\mx\managers\ToolTipManagerImpl.as:1146]
    at mx.managers::ToolTipManagerImpl/http://www.adobe.com/2006/flex/mx/internal::targetChanged()[E:\dev\4.x\frameworks\projects \framework\src\mx\managers\ToolTipManagerImpl.as:852]
    at mx.managers::ToolTipManagerImpl/http://www.adobe.com/2006/flex/mx/internal::checkIfTargetChanged()[E:\dev\4.x\frameworks\p rojects\framework\src\mx\managers\ToolTipManagerImpl.as:744]
    at mx.managers::ToolTipManagerImpl/http://www.adobe.com/2006/flex/mx/internal::toolTipMouseOverHandler()[E:\dev\4.x\framework s\projects\framework\src\mx\managers\ToolTipManagerImpl.as:1565]
some of the tooltip:
<?xml version="1.0" encoding="utf-8"?>
<mx:Panel xmlns:fx="http://ns.adobe.com/mxml/2009" implements="mx.core.IToolTip"
          xmlns:s="library://ns.adobe.com/flex/spark"
          xmlns:mx="library://ns.adobe.com/flex/mx" layout="absolute" width="400" height="300">
    <fx:Declarations>
        <!-- Place non-visual elements (e.g., services, value objects) here -->
    </fx:Declarations>
    <fx:Script>
        <![CDATA[
            import mx.core.IToolTip;
            [Bindable]
            public var dataItem:Object;
            //  Implement required methods of the IToolTip interface; these
            //  methods are not used in this example, though.
            public var _text:String;
            public function get text():String {
                return _text;
            public function set text(value:String):void {
        ]]>
    </fx:Script>
    <mx:Image source="http://intranet/Intranet/EmployeeSearch/images/{dataItem.staffID}.jpg"/>
    <mx:Form paddingBottom="10" paddingLeft="10" paddingRight="10" paddingTop="10" verticalGap="1">
        <mx:FormItem label="Branch name">
            <mx:Label text="dataItem.NAME"/></mx:FormItem>
        <mx:FormItem label="Staff name">
            <mx:Label text="{dataItem.staffName}"/></mx:FormItem>
        <mx:FormItem label="Excessive Wait">
            <mx:Label text="{dataItem.wasExcessiveWait}"/></mx:FormItem>
        <mx:FormItem label="Eye contact">
            <mx:Label text="{dataItem.wasEyeContact}"/></mx:FormItem>
        <mx:FormItem label="Commission">
            <mx:Label text="{dataItem.commision}"/></mx:FormItem>
        <mx:FormItem label="Ex-Rate">
            <mx:Label text="{dataItem.exchangeRate}"/></mx:FormItem>
        <mx:FormItem label="Round up &gt; £5">
            <mx:Label text="{dataItem.wasRoundUp}"/></mx:FormItem>
        <mx:FormItem label="Trade-up attempted">
            <mx:Label text="{dataItem.wasTradeUpAttempted}"/></mx:FormItem>
        <mx:FormItem label="Offered other products">
            <mx:Label text="{dataItem.OfferedOtherProducts}"/></mx:FormItem>
        <mx:FormItem label="Wallet offered">
            <mx:Label text="{dataItem.wasWallet}"/></mx:FormItem>
        <mx:FormItem label="Thank you">
            <mx:Label text="{dataItem.wasThankYou}"/></mx:FormItem>
        <mx:FormItem label="Wished Pleasant Trip/Day">
            <mx:Label text="{dataItem.wasWishedPleasantTrip}"/></mx:FormItem>
        <mx:FormItem label="Branch appearance">
            <mx:Label text="{dataItem.branchAppearance}"/></mx:FormItem>
        <mx:FormItem label="Customer service">
            <mx:Label text="{dataItem.customerService}"/></mx:FormItem>
        <mx:FormItem label="userID">
            <mx:Label text="{dataItem.userID}"/></mx:FormItem>
    </mx:Form>
</mx:Panel>

Answer 1

I got round it by doing this:
    <s:Label text="Data" id="Comment" >
                                                <s:toolTipCreate>
                                                    <![CDATA[
                                                    var toolTip:pa = new pa();
                                                    toolTip.dataItem = data;
                                                    event.toolTip = toolTip;
                                                    ]]>
                                                </s:toolTipCreate>
                                            </s:Label>