invocation of rpc via restconf fails because of whitespace

By deleting group via restconf (operations):

http://localhost:8080/restconf/operations/sal-group:remove-group
– This works –
POST:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<input xmlns="urn:opendaylight:group:service">
<barrier>false</barrier>
<group-id>1</group-id>
<group-name>Foo</group-name>
<group-type>group-select</group-type>

<node xmlns:inv="urn:opendaylight:inventory">/inv:nodes/inv:node[inv:id="openflow:1"]</node>
</input>

Response:
{
"output":

}

– But this fails –
POST:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<input xmlns="urn:opendaylight:group:service">
<barrier>false</barrier>
<group-id>1</group-id>
<group-name>Foo</group-name>
<group-type>group-select</group-type>

<node xmlns:inv="urn:opendaylight:inventory">
/inv:nodes/inv:node[inv:id="openflow:1"]
</node>
</input>

Response:

• • • • • HTTP Status 500 - ******
          ===============================================================================
          type Exception report
          message
          description The_server_encountered_an_internal_error_that_prevented_it_from
          fulfilling_this_request.
          exception
          java.lang.IllegalArgumentException
          com.google.common.base.Preconditions.checkArgument(Preconditions.java:76)
          org.opendaylight.controller.sal.dom.broker.impl.SchemaAwareRpcBroker$RoutedRpcSelector.invokeRpc
          (SchemaAwareRpcBroker.java:329)
          org.opendaylight.controller.sal.dom.broker.impl.SchemaAwareRpcBroker.invokeRpc
          (SchemaAwareRpcBroker.java:168)
          org.opendaylight.controller.sal.dom.broker.BrokerImpl.invokeRpcAsync
          (BrokerImpl.java:116)
          org.opendaylight.controller.sal.dom.broker.ConsumerContextImpl.rpc
          (ConsumerContextImpl.java:65)
          org.opendaylight.controller.sal.restconf.impl.BrokerFacade.invokeRpc
          (BrokerFacade.java:128)
          org.opendaylight.controller.sal.restconf.impl.RestconfImpl.callRpc
          (RestconfImpl.java:624)
          org.opendaylight.controller.sal.restconf.impl.RestconfImpl.invokeRpc
          (RestconfImpl.java:566)
          ...