How to right use Split EIP by xpath in my case?

Example data:

<bookstore>
    <book category="COOKING"/>
    <book category="CHILDREN"/>
    <book category="WEB"/>
</bookstore>

What is the right way to process in for-loop values of attribute “category” of “book” node?
Why is my route doesn’t work correctly?

<route>
    <from uri="..."/>
    <split>
        <xpath>//book/@category</xpath>
        <log message="body = ${body}"/>
    </split>
</route>

The log contains an empty body 3 times. The body class is com.sun.org.apache.xerces.internal.dom.DeferredAttrNSImpl.

• Do I miss some dependencies that contain the correct type converter from attribute to String?
• Should I define converter by myself?
• Should I split by //book nodes and inside set body with xpath “/*/@category” (yes, it’s works correctly).
• Is it a bug?

I want to understand why it work like that and what a correct way to solve?

P.S. convertBodyTo doesn’t help

P.P.S. Working, but less readable solutuion (body type com.sun.org.apache.xml.internal.dtm.ref.DTMNodeList)

<route>
    <from uri="..."/>
    <split>
        <xpath>//book</xpath>
        <setBody>
            <xpath>/*/@category</xpath>
        </setBody>
        <log message="body = ${body}"/>
    </split>
</route>