esb - logger print null but echo print message in mule flow -

i iterating xml in foreach. echo printing correct message logger print null.

<foreach collection="#[xpath('//xmlsoap/soap/soapenv:envelope')]"             doc:name="for each">             <echo-component />             <logger level="info" category="protsp logger" message="#[payload]"             doc:name="logger" />         </foreach> 

i resolved problem using dom xml transformer.

<foreach collection="#[xpath('//xmlsoap/soap/soapenv:envelope')]"             doc:name="for each">              <echo-component doc:name="echo"/>             <mulexml:dom-to-xml-transformer doc:name="dom xml"/>                <logger level="info" category="protsp logger" message="#[payload]"                 doc:name="logger" />         </foreach>