Send Mediator with VFS error WSO2 ESB - wso2

Question

I create a proxy and sequence to read file from source folder then write it to target folder with send mediator with VFS. My Proxy look like this :
<proxy name="XXX" transports="vfs" startOnLoad="true" trace="disable">
<description/>
<target>
<inSequence>
<property name="filename"
expression="fn:concat(get-property('transport', 'FILE_NAME'), '')"/>
<sequence key="write"/>
<log level="custom">
<property name="finish" value="finish"/>
</log>
</inSequence>
</target>
<parameter name="transport.PollInterval">1</parameter>
<parameter name="transport.vfs.ActionAfterProcess">MOVE</parameter>
<parameter name="transport.vfs.MoveAfterProcess">file:///after</parameter>
<parameter name="transport.vfs.FileURI">file:///process</parameter>
<parameter name="transport.vfs.FileNamePattern">.*.txt</parameter>
<parameter name="transport.vfs.ContentType">text/plain</parameter>
and my "write" sequence look like this :
<sequence name="write">
<property name="transport.vfs.ReplyFileName"
expression="get-property('filename')"
scope="transport"/>
<property name="OUT_ONLY" value="true"/>
<send>
<endpoint name="FileEpr">
<address uri="vfs:file:///Target"/>
</endpoint>
</send>
When I tried this proxy and sequence, the send mediator success to create a file in the "target" folder, but the problem is the content of the file is not written. So the size is 0 byte. My original file is 1000bytes. If I add this config in the sequence
<log level="full"/>
it works perfectly fine. My question is, do I need to use the log full config? but when I look at the File Processing sample in WSO2 web it doesn't use any log full config. So how can I use send mediator to write file without using any "log" property?
Thanks,