Failed to prepare candidate. Failed to initialize transaction

Steps to reproduce the bug
Configure BGP through netconf
-RIb
-rrclient
and wait for at least 1 minute

<errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
<error>
<error-type>application</error-type>
<error-tag>operation-failed</error-tag>
<error-message>Error updating data </error-message>
<error-info>java.lang.RuntimeException: RemoteDevice

{controller-config}: Failed to prepare candidate. Failed to initialize transaction
at org.opendaylight.netconf.sal.connect.netconf.sal.tx.WriteCandidateTx.init(WriteCandidateTx.java:92)
at org.opendaylight.netconf.sal.connect.netconf.sal.tx.AbstractWriteTx.<init>(AbstractWriteTx.java:52)
at org.opendaylight.netconf.sal.connect.netconf.sal.tx.WriteCandidateTx.<init>(WriteCandidateTx.java:75)
at org.opendaylight.netconf.sal.connect.netconf.sal.NetconfDeviceDataBroker.newWriteOnlyTransaction(NetconfDeviceDataBroker.java:74)
at org.opendaylight.netconf.sal.connect.netconf.sal.NetconfDeviceDataBroker.newReadWriteTransaction(NetconfDeviceDataBroker.java:65)
at org.opendaylight.netconf.sal.restconf.impl.BrokerFacade.commitConfigurationDataPut(BrokerFacade.java:121)
at org.opendaylight.netconf.sal.restconf.impl.RestconfImpl.updateConfigurationData(RestconfImpl.java:723)
at org.opendaylight.netconf.sal.restconf.impl.StatisticsRestconfServiceWrapper.updateConfigurationData(StatisticsRestconfServiceWrapper.java:133)
at org.opendaylight.netconf.sal.rest.impl.RestconfCompositeWrapper.updateConfigurationData(RestconfCompositeWrapper.java:82)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205)
at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302)
at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
at com.sun.jersey.server.impl.uri.rules.ResourceObjectRule.accept(ResourceObjectRule.java:100)
at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1511)
at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1442)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1391)
at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1381)
at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:538)
at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:716)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:684)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1496)
at org.eclipse.jetty.servlets.CrossOriginFilter.handle(CrossOriginFilter.java:247)
at org.eclipse.jetty.servlets.CrossOriginFilter.doFilter(CrossOriginFilter.java:210)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1467)
at org.eclipse.jetty.servlets.UserAgentFilter.doFilter(UserAgentFilter.java:82)
at org.eclipse.jetty.servlets.GzipFilter.doFilter(GzipFilter.java:256)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1467)
at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1467)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:501)
at org.ops4j.pax.web.service.jetty.internal.HttpServiceServletHandler.doHandle(HttpServiceServletHandler.java:69)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:557)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
at org.ops4j.pax.web.service.jetty.internal.HttpServiceContext.doHandle(HttpServiceContext.java:240)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:429)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
at org.ops4j.pax.web.service.jetty.internal.JettyServerHandlerCollection.handle(JettyServerHandlerCollection.java:75)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
at org.eclipse.jetty.server.Server.handle(Server.java:370)
at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:494)
at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:982)
at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1043)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)
at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:696)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:53)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
at java.lang.Thread.run(Thread.java:745)
Caused by: NetconfDocumentedException{message=RemoteDevice{controller-config}

: Lock candidate failed: [RpcError [message=The netconf session to controller-config is disconnected, severity=ERROR, errorType=TRANSPORT, tag=operation-failed, applicationTag=null, info=null, cause=null]], errorType=application, errorTag=operation_failed, errorSeverity=warning, errorInfo={}}
at org.opendaylight.netconf.sal.connect.netconf.sal.tx.AbstractWriteTx.invokeBlocking(AbstractWriteTx.java:71)
at org.opendaylight.netconf.sal.connect.netconf.sal.tx.WriteCandidateTx.lock(WriteCandidateTx.java:100)
at org.opendaylight.netconf.sal.connect.netconf.sal.tx.WriteCandidateTx.init(WriteCandidateTx.java:89)
... 63 more
</error-info>
</error>
</errors>