Unable to save new data via POST operation in XML format behind mount point

1. 1. 500 error saving new data via POST operation in XML format behind mount point ##

Using SP edition

org.opendaylight.controller.version = 0.1
org.opendaylight.controller.build.scm.version = 244e40365da433da8b29fa2affbaf7886d4addf9
org.opendaylight.controller.build.user = jenkins-controller
org.opendaylight.controller.build.workspace = **********
org.opendaylight.controller.build.timestamp = 1408665033577
org.opendaylight.controller.build.machine = **********

1. 1. Step 1 Confirm "controller-config" is present

GET http://localhost:8080/restconf/config/opendaylight-inventory:nodes/node/controller-config

returns data

<node xmlns="urn:opendaylight:inventory"><id>controller-config</id></node>

1. 1. Step 2

HTTP operation: POST

URI pattern: http://localhost:8080/restconf/config/opendaylight-inventory:nodes/node/controller-config/yang-ext:mount/config:modules

Payload:

<module xmlns="urn:opendaylight:params:xml:ns:yang:controller:config">
<name>test21</name>
</module>

1. 1. Expected Result
      HTTP status 204 and data is mounted.

1. 1. Actual Result

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<errors
xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
<error>
<error-type>application</error-type>
<error-tag>operation-failed</error-tag>
<error-message>Failed to read pre-existing data</error-message>
<error-info>ReadFailedException

{message=Exists failed, errorList=[RpcError [message=Exists failed, severity=ERROR, errorType=APPLICATION, tag=operation-failed, applicationTag=null, info=null, cause=java.util.concurrent.ExecutionException: java.lang.IllegalArgumentException: It wasn't possible to get namespace for prefix prefix]]}

at org.opendaylight.controller.sal.connect.netconf.sal.tx.NetconfDeviceReadWriteTx.exists(NetconfDeviceReadWriteTx.java:84)

...
</error-info>
</error>
</errors>