Steps to reproduce
Put attached file “regexp-module.yang” to your schema directory.
Run simulated device 
•	:~/netconf/netconf/tools/netconf-testtool/target$ 
java -jar netconf-testtool-2.0.10-SNAPSHOT-executable.jar --debug true --schemas-dir ~/test-schemas/
Run ODL
•	:~/netconf/karaf/target/assembly/bin$ ./karaf
•	install features:
	- odl-netconf-topology
	- odl-restconf-nb-rfc8040
	- odl-mdsal-apidocs
Send this request (I recommed to use Postman)
PUT http://localhost:8181/rests/data/network-topology:network-topology/topology=topology-netconf/node=device-17830
Headers:
•	Content-Type : application/json
•	Accept : application/json
Authorization : basic (admin:admin)

Body:
{
    "node": [
        {
            "node-id": "device-17830",
		"netconf-node-topology:port": 17830,
            "netconf-node-topology:reconnect-on-changed-schema": false,
            "netconf-node-topology:connection-timeout-millis": 20000,
            "netconf-node-topology:tcp-only": false,
            "netconf-node-topology:max-connection-attempts": 0,
            "netconf-node-topology:username": "admin",
            "netconf-node-topology:password": "admin",
            "netconf-node-topology:sleep-factor": 1.5,
            "netconf-node-topology:host": "127.0.0.1",
            "netconf-node-topology:between-attempts-timeout-millis": 2000,
            "netconf-node-topology:keepalive-delay": 120
        }
    ]
}

Open this site in your browser:
http://localhost:8181/apidoc/explorer/index.html
Click on dropdown list and select your mounted device. 

Try to choose both, RestConf RFC 8040 and RestConf draft02. (Sometimes list is shown, but when you try both options multiple times it will throw fetch error.)
You should see following fetch error:

When you check your karaf.log file, you should see StackOverFlow error. My logs will be attached in bug description.