Making declarative design from java code

Hello guys, I am new to Vaadin and java,
I got a project from other developer with complex UIs, built in java code without using declarative design.
It is very difficult to modify such UIs.
I tried to get declarative design using debug window (Button - Generate declarative design for the given component subtree).
But in Eclipse console (Tomcat server) i got

янв 05, 2018 7:50:37 PM com.vaadin.server.DefaultErrorHandler doDefault
SEVERE:
com.vaadin.ui.declarative.DesignException: Could not create component test.testUI.ModeView
at com.vaadin.ui.declarative.Design$DefaultComponentFactory.createComponent(Design.java:176)
at com.vaadin.ui.declarative.DesignContext.instantiateClass(DesignContext.java:590)
at com.vaadin.ui.declarative.DesignContext.getDefaultInstance(DesignContext.java:373)
at com.vaadin.ui.declarative.DesignContext.getDefaultInstance(DesignContext.java:366)
at com.vaadin.ui.AbstractComponent.writeDesign(AbstractComponent.java:1306)
at com.vaadin.ui.AbstractOrderedLayout.writeDesign(AbstractOrderedLayout.java:527)
at com.vaadin.ui.declarative.DesignContext.createElement(DesignContext.java:479)
at com.vaadin.ui.declarative.Design.createHtml(Design.java:530)
at com.vaadin.ui.declarative.Design.write(Design.java:754)
at com.vaadin.ui.declarative.Design.write(Design.java:733)
at com.vaadin.ui.UI$2.showServerDesign(UI.java:230)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:158)
at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:119)
at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:437)
at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:402)
at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:273)
at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:90)
at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1435)
at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:380)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:94)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:502)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1132)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1539)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1495)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.InstantiationException: test.testUI.ModeView
at java.lang.Class.newInstance(Class.java:427)
at com.vaadin.ui.declarative.Design$DefaultComponentFactory.createComponent(Design.java:174)
… 45 more
Caused by: java.lang.NoSuchMethodException: test.testUI.ModeView.()
at java.lang.Class.getConstructor0(Class.java:3082)
at java.lang.Class.newInstance(Class.java:412)
… 46 more

what is wrong?
If i get declarative, i can try Vaadin Designer