Traversing node using xpath

How do I write xpath query for the node below? I need to traverse the tree until child "Attribute" is not null.

<Attribute name="ParentNode开发者_JAVA技巧" type="collection" datatype="collection" value="">
   <Attribute name="ChildNode" type="collection" datatype="collection" value="">
     <Attribute name="GrandChild" type="Measurable.Text" datatype="string" value="2605"/>
   </Attribute>
</Attribute> 

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Try this Xpath expression: //Attribute[not(*)].