Restconf: Not working GET operation on mount points

GET: http://localhost:8181/restconf/15/data/network-topology:network-topology/topology=topology-netconf/node=device1/yang-ext:mount

result:
{
"errors": {
"error": [

{ "error-type": "application", "error-tag": "operation-failed", "error-message": "Bad type of node." }

]
}
}