Navigate to a new view upon click using flex

friends. I'm developing a flex mobile app. I've declared a Titlewindow which contains the alert message following the example of "TourdeFlex". And I failed to navigate to a new View after clicking YES button.

<fx:Script>
    <![CDATA[
           protected function some_handler():开发者_JAVA技巧void
           {
              (new AlertMsg()).open(this,false);
           }
    ]]>
</fx:Script>        
    <fx:Declarations>
    <fx:Component className="AlertMsg">
        <s:SkinnablePopUpContainer x="70" y="300">


            <s:TitleWindow title="MSG" close="close()">
                <s:VGroup horizontalAlign="center" paddingTop="8" paddingBottom="8" paddingLeft="8" paddingRight="8" gap="5" width="100%">
                    <s:Label text="Some Alert MSG"/>
                    <s:HGroup>
                        <s:Button label="YES" click="{outerDocument.navigator.pushView(myNewView)}"/>
                        <s:Button label="No" click="close()"/>
                    </s:HGroup>

                </s:VGroup>
            </s:TitleWindow>
        </s:SkinnablePopUpContainer>
    </fx:Component>

</fx:Declarations>

This code can be successfully compiled but it was wrong during runtime:Error #1009: Cannot access a property or method of a null object reference. How can I handle this kind of problem.

outerDocument is null. Try owner:

click="(owner as spark.components.View).navigator.pushView(myNewView)"