WSO2 clustering APIM and DAS with mysql,did not show stats with this error

1. Clustering APIM divide into 4 part,publisher,store,keymanager, gataway. And use DAS for stats. Database is mysql.

2. I set the connection between APIM and DAS on publisher node.

3. When I invoke an api ,APIM console give error as below.

 [2016-10-13 11:13:54,775] ERROR - APIMgtUsageHandler Cannot publish event. null
java.lang.NullPointerException
        at org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageDataBridgeDataPublisher.publishEvent(APIMgtUsageDataBridgeDataPublisher.java:124)
        at org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageHandler.handleRequest(APIMgtUsageHandler.java:169)
        at org.apache.synapse.rest.API.process(API.java:322)
        at org.apache.synapse.rest.RESTRequestHandler.dispatchToAPI(RESTRequestHandler.java:86)
        at org.apache.synapse.rest.RESTRequestHandler.process(RESTRequestHandler.java:65)
        at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.injectMessage(Axis2SynapseEnvironment.java:295)
        at org.apache.synapse.core.axis2.SynapseMessageReceiver.receive(SynapseMessageReceiver.java:83)
        at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
        at org.apache.synapse.transport.passthru.ServerWorker.processNonEntityEnclosingRESTHandler(ServerWorker.java:317)
        at org.apache.synapse.transport.passthru.ServerWorker.run(ServerWorker.java:149)
        at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
[2016-10-13 11:13:54,807] ERROR - APIMgtResponseHandler Cannot publish response event. null
java.lang.NullPointerException
        at org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageDataBridgeDataPublisher.publishEvent(APIMgtUsageDataBridgeDataPublisher.java:140)
        at org.wso2.carbon.apimgt.usage.publisher.APIMgtResponseHandler.mediate(APIMgtResponseHandler.java:211)
        at org.apache.synapse.mediators.ext.ClassMediator.mediate(ClassMediator.java:84)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:81)
        at org.apache.synapse.mediators.AbstractListMediator.mediate(AbstractListMediator.java:48)
        at org.apache.synapse.mediators.base.SequenceMediator.mediate(SequenceMediator.java:155)
        at org.apache.synapse.rest.Resource.process(Resource.java:297)
        at org.apache.synapse.rest.API.process(API.java:335)
        at org.apache.synapse.rest.RESTRequestHandler.dispatchToAPI(RESTRequestHandler.java:86)
        at org.apache.synapse.rest.RESTRequestHandler.process(RESTRequestHandler.java:52)
        at org.apache.synapse.core.axis2.Axis2SynapseEnvironment.injectMessage(Axis2SynapseEnvironment.java:295)
        at org.apache.synapse.core.axis2.SynapseCallbackReceiver.handleMessage(SynapseCallbackReceiver.java:529)
        at org.apache.synapse.core.axis2.SynapseCallbackReceiver.receive(SynapseCallbackReceiver.java:172)
        at org.apache.axis2.engine.AxisEngine.receive(AxisEngine.java:180)
        at org.apache.synapse.transport.passthru.ClientWorker.run(ClientWorker.java:251)
        at org.apache.axis2.transport.base.threads.NativeWorkerPool$1.run(NativeWorkerPool.java:172)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

In order to slove this problem ,I get in touch with the dev of wso2.

rukshan gives me this solution,configure DAS on api-manager.xml ,not on the UI.