JsonPaintTarget NullPointer Exception

3.05.2016 10:57:55 com.vaadin.server.DefaultErrorHandler doDefault
SCHWERWIEGEND: 
java.lang.RuntimeException: Push failed
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:171)
    at com.vaadin.server.communication.PushHandler$2.run(PushHandler.java:150)
    at com.vaadin.server.communication.PushHandler.callWithUi(PushHandler.java:243)
    at com.vaadin.server.communication.PushHandler.onMessage(PushHandler.java:503)
    at com.vaadin.server.communication.PushAtmosphereHandler.onMessage(PushAtmosphereHandler.java:88)
    at com.vaadin.server.communication.PushAtmosphereHandler.onRequest(PushAtmosphereHandler.java:78)
    at org.atmosphere.cpr.AsynchronousProcessor.action(AsynchronousProcessor.java:199)
    at org.atmosphere.cpr.AsynchronousProcessor.suspended(AsynchronousProcessor.java:107)
    at org.atmosphere.container.TomcatWebSocketUtil.doService(TomcatWebSocketUtil.java:154)
    at org.atmosphere.container.Tomcat7Servlet30SupportWithWebSocket.service(Tomcat7Servlet30SupportWithWebSocket.java:62)
    at org.atmosphere.cpr.AtmosphereFramework.doCometSupport(AtmosphereFramework.java:2075)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:571)
    at org.atmosphere.websocket.DefaultWebSocketProcessor$3.run(DefaultWebSocketProcessor.java:333)
    at org.atmosphere.util.VoidExecutorService.execute(VoidExecutorService.java:101)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:328)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:425)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatchReader(DefaultWebSocketProcessor.java:795)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:527)
    at org.atmosphere.container.TomcatWebSocketHandler.onTextData(TomcatWebSocketHandler.java:104)
    at org.apache.catalina.websocket.StreamInbound.doOnTextData(StreamInbound.java:191)
    at org.apache.catalina.websocket.StreamInbound.onData(StreamInbound.java:139)
    at org.apache.coyote.http11.upgrade.UpgradeProcessor.upgradeDispatch(UpgradeProcessor.java:88)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:621)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException: Parameters must be non-null strings
    at com.vaadin.server.JsonPaintTarget.addAttribute(JsonPaintTarget.java:381)
    at com.vaadin.event.dd.acceptcriteria.ClientSideCriterion.paint(ClientSideCriterion.java:56)
    at com.vaadin.ui.DragAndDropWrapper.paintContent(DragAndDropWrapper.java:262)
    at com.vaadin.server.LegacyPaint.paint(LegacyPaint.java:65)
    at com.vaadin.server.communication.LegacyUidlWriter.write(LegacyUidlWriter.java:82)
    at com.vaadin.server.communication.UidlWriter.write(UidlWriter.java:145)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:168)
    ... 27 more
13.05.2016 10:57:55 com.vaadin.server.communication.PushHandler callWithUi
WARNUNG: Error while unlocking session
java.lang.RuntimeException: Push failed
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:171)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:146)
    at com.vaadin.ui.UI.push(UI.java:1551)
    at com.vaadin.server.VaadinSession.unlock(VaadinSession.java:997)
    at com.vaadin.server.communication.PushHandler.callWithUi(PushHandler.java:271)
    at com.vaadin.server.communication.PushHandler.onMessage(PushHandler.java:503)
    at com.vaadin.server.communication.PushAtmosphereHandler.onMessage(PushAtmosphereHandler.java:88)
    at com.vaadin.server.communication.PushAtmosphereHandler.onRequest(PushAtmosphereHandler.java:78)
    at org.atmosphere.cpr.AsynchronousProcessor.action(AsynchronousProcessor.java:199)
    at org.atmosphere.cpr.AsynchronousProcessor.suspended(AsynchronousProcessor.java:107)
    at org.atmosphere.container.TomcatWebSocketUtil.doService(TomcatWebSocketUtil.java:154)
    at org.atmosphere.container.Tomcat7Servlet30SupportWithWebSocket.service(Tomcat7Servlet30SupportWithWebSocket.java:62)
    at org.atmosphere.cpr.AtmosphereFramework.doCometSupport(AtmosphereFramework.java:2075)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:571)
    at org.atmosphere.websocket.DefaultWebSocketProcessor$3.run(DefaultWebSocketProcessor.java:333)
    at org.atmosphere.util.VoidExecutorService.execute(VoidExecutorService.java:101)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:328)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:425)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatchReader(DefaultWebSocketProcessor.java:795)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:527)
    at org.atmosphere.container.TomcatWebSocketHandler.onTextData(TomcatWebSocketHandler.java:104)
    at org.apache.catalina.websocket.StreamInbound.doOnTextData(StreamInbound.java:191)
    at org.apache.catalina.websocket.StreamInbound.onData(StreamInbound.java:139)
    at org.apache.coyote.http11.upgrade.UpgradeProcessor.upgradeDispatch(UpgradeProcessor.java:88)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:621)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException: Parameters must be non-null strings
    at com.vaadin.server.JsonPaintTarget.addAttribute(JsonPaintTarget.java:381)
    at com.vaadin.event.dd.acceptcriteria.ClientSideCriterion.paint(ClientSideCriterion.java:56)
    at com.vaadin.ui.DragAndDropWrapper.paintContent(DragAndDropWrapper.java:262)
    at com.vaadin.server.LegacyPaint.paint(LegacyPaint.java:65)
    at com.vaadin.server.communication.LegacyUidlWriter.write(LegacyUidlWriter.java:82)
    at com.vaadin.server.communication.UidlWriter.write(UidlWriter.java:145)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:168)
    ... 29 more
13.05.2016 10:57:55 com.vaadin.server.communication.PushHandler callWithUi
WARNUNG: Error while ending request
java.lang.RuntimeException: Push failed
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:171)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:146)
    at com.vaadin.ui.UI.push(UI.java:1551)
    at com.vaadin.server.VaadinSession.unlock(VaadinSession.java:997)
    at com.vaadin.server.VaadinService.requestEnd(VaadinService.java:1356)
    at com.vaadin.server.communication.PushHandler.callWithUi(PushHandler.java:281)
    at com.vaadin.server.communication.PushHandler.onMessage(PushHandler.java:503)
    at com.vaadin.server.communication.PushAtmosphereHandler.onMessage(PushAtmosphereHandler.java:88)
    at com.vaadin.server.communication.PushAtmosphereHandler.onRequest(PushAtmosphereHandler.java:78)
    at org.atmosphere.cpr.AsynchronousProcessor.action(AsynchronousProcessor.java:199)
    at org.atmosphere.cpr.AsynchronousProcessor.suspended(AsynchronousProcessor.java:107)
    at org.atmosphere.container.TomcatWebSocketUtil.doService(TomcatWebSocketUtil.java:154)
    at org.atmosphere.container.Tomcat7Servlet30SupportWithWebSocket.service(Tomcat7Servlet30SupportWithWebSocket.java:62)
    at org.atmosphere.cpr.AtmosphereFramework.doCometSupport(AtmosphereFramework.java:2075)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:571)
    at org.atmosphere.websocket.DefaultWebSocketProcessor$3.run(DefaultWebSocketProcessor.java:333)
    at org.atmosphere.util.VoidExecutorService.execute(VoidExecutorService.java:101)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:328)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:425)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatchReader(DefaultWebSocketProcessor.java:795)
    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:527)
    at org.atmosphere.container.TomcatWebSocketHandler.onTextData(TomcatWebSocketHandler.java:104)
    at org.apache.catalina.websocket.StreamInbound.doOnTextData(StreamInbound.java:191)
    at org.apache.catalina.websocket.StreamInbound.onData(StreamInbound.java:139)
    at org.apache.coyote.http11.upgrade.UpgradeProcessor.upgradeDispatch(UpgradeProcessor.java:88)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:621)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException: Parameters must be non-null strings
    at com.vaadin.server.JsonPaintTarget.addAttribute(JsonPaintTarget.java:381)
    at com.vaadin.event.dd.acceptcriteria.ClientSideCriterion.paint(ClientSideCriterion.java:56)
    at com.vaadin.ui.DragAndDropWrapper.paintContent(DragAndDropWrapper.java:262)
    at com.vaadin.server.LegacyPaint.paint(LegacyPaint.java:65)
    at com.vaadin.server.communication.LegacyUidlWriter.write(LegacyUidlWriter.java:82)
    at com.vaadin.server.communication.UidlWriter.write(UidlWriter.java:145)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:168)
    ... 30 more
java.lang.RuntimeException: Push failed
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:171)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:146)
    at com.vaadin.ui.UI.push(UI.java:1551)
    at com.vaadin.server.VaadinSession.unlock(VaadinSession.java:997)
    at com.vaadin.server.VaadinService.requestEnd(VaadinService.java:1356)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1423)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:364)
    at de.alfa.openMedia.adSuite.vaadin.AdSuiteVaadinApplicationServlet.service(AdSuiteVaadinApplicationServlet.java:53)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:122)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:169)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException: Parameters must be non-null strings
    at com.vaadin.server.JsonPaintTarget.addAttribute(JsonPaintTarget.java:381)
    at com.vaadin.event.dd.acceptcriteria.ClientSideCriterion.paint(ClientSideCriterion.java:56)
    at com.vaadin.ui.DragAndDropWrapper.paintContent(DragAndDropWrapper.java:262)
    at com.vaadin.server.LegacyPaint.paint(LegacyPaint.java:65)
    at com.vaadin.server.communication.LegacyUidlWriter.write(LegacyUidlWriter.java:82)
    at com.vaadin.server.communication.UidlWriter.write(UidlWriter.java:145)
    at com.vaadin.server.communication.AtmospherePushConnection.push(AtmospherePushConnection.java:168)
    ... 27 more