Failed to maps instance-identifier (XML node) into Java InstanceIdentifier

java.lang.ClassCastException: java.lang.String cannot be cast to org.opendaylight.yangtools.yang.data.api.InstanceIdentifier

yang module snippet:
leaf path {
type instance-identifier;
}

xml input snippet:
<path xmlns:topo="urn:TBD:params:xml:ns:yang:network-topology">/topo:network-topology/topo:topology[topo:topology-id="pcep-topology"]</path>