AppEngine+GWT-RPC+搜索API提供错误

Question

IndexSpec indexSpec = IndexSpec.newBuilder().setName("index").build(); 
Index index = SearchServiceFactory.getSearchService().getIndex(indexSpec);
Document doc = Document.newBuilder()...
try{
    index.put(doc); //Line that results in an exception
}catch(Exception e){
    e.printStackTrace();
}

StackTrace：

com.google.apphosting.API.apiproxy$CallNotFoundException：如果线程既不是原始请求线程，也不是ThreadManager在com.google.apphosting.API.apiproxy$callNotFoundException.ForeignThread(approxy.java:800)在com.google.apphosting.API.apiproxy$1创建的线程，则无法使API调用Search.IndexDocument。get(approxy.java:175)在com.google.apphosting.API.apiproxy$1。在com.google.appengine.appengine.API.search.futureHelper.getInternal(FutureHelper.java:73)，在com.google.appengine.API.search.futureHelper.quietget(FutureHelper.java:32)，在com.google.appengine.API.search.indeximpl.put(indeximpl.java:485)，在com.vehicle.track.server.user.save(user.java:82)，在EmethodAccessorImpl.java:62)位于sun.reflect.delegatingMethodAccessorImpl.invoke（delegatingMethodAccessorImpl.java：43）在java.lang.reflect.method.invoke（method.java：498）在com.google.gwt.user.server.rpc.rpc.invokeandEncoderEsponse（rpc.java：587）在com.google.gwt.user.server.rpc.remoteserviceServlet.processCall（remoteserviceServlet.java：333)，在.remoteserviceservlet.processPost（remoteserviceservlet.java：373）在com.google.gwt.user.server.rpc.abstractremoteserviceservlet.doPost（abstractremoteserviceservlet.java：62）在javax.servlet.http.httpservlet.service（httpservlet.java：707）在javax.servlet.http.httpservlet.java：790）在org.eclipse.jetty.servlet.servlet.handle（servlethandler.doHandle（java:587)在org.eclipse.jetty.server.handler.scopedhandler.handle（scopedhandler.java:143)在org.eclipse.jetty.security.securityHandler.handle(securityHandler.java:577)在org.eclipse.jetty.server.session.sessionHandler.doHandle(sessionHandler.java:223)在org.eclipse.jetty.server.handler.contexthandler.doHandle(contexthandler.java:1127)在org.eclipse.jetty.servlet.servlet.doScope(servlethandler.java:515)在在org.eclipse.jetty.server.handler.scopedHandler.handler(scopedHandler.java:141)，org.eclipse.jetty.server.handler.handler.handler(handlerWrapper.handler(handlerWrapper.java:97)，org.eclipse.jetty.server.handler.java:95)，org.eclipse.jetty.handler.handler.handler(org.eclipse.jetty.handler.handler.handler.java:499)在org.eclipse.jetty.server.httpchannel.handle(httpchannel.java:311)在org.eclipse.jetty.server.httpconnection.onfillable(httpconnection.java:257）在org.eclipse.jetty.io.abstractConnection$2.run(abstractConnection.java:544)在org.eclipse.jetty.util.thread.queuedThreadPool.runjob(queuedThreadPool.java:635)在org.eclipse.jetty.util.thread.queuedThreadPool.java:635)在java.lang.thread.run(thread.java:748)在