xml.content return null

<krpano onstart="trace(get(xml.content))">


  
   <preview type="grid(cube,16,16,512,0xCCCCCC,0xFFFFFF,0x999999);" details="16" />


   <layer name="bt1" type="container"  bgalpha="1" bgcolor="0x993322" align="center" width="100" height="20" x="-150" bgcapture="true" onclick="switch(width,100,50)" onhover="tween(bgcolor,0xCC66FF)" onout="tween(bgcolor,0x993322)" onover=""/>




   <layer name="bt2" type="container" bgalpha="1" bgcolor="0xDD3322" align="center" width="100" height="20" x="150" bgcapture="true" onclick="callwith(layer[bt1],onclick);" onhover="callwith(layer[bt1],onhover);" onout="callwith(layer[bt1],onout);"/>


   <layer name="bt3" type="container"  bgalpha="1" bgcolor="0xAA3322" align="center" width="100" height="20" x="300" bgcapture="true" onclick="callwith(layer[bt1],add(height,20));trace(get(xml.url))" />


   <plugin name="hotspot_pos_info"
        url="%SWFPATH%/plugins/textfield.swf"
        html=""
        css="font-family:Courier;"
        padding="8"
        align="lefttop" x="10" y="10"
        width="200"
        enabled="false"
        />	




</krpano>