When a field included in the form whithin a switchable field is required, there's an error when committing if switchable field has not been even clicked.

Steps to reproduce:

1. Use the following dialog definition:

   form:
     properties:
       switchable:
         $type: switchableField
         field:
           $type: radioButtonGroupField
           layout: horizontal
           datasource:
             $type: optionListDatasource
             options:
               - name: foo
                 value: foo
               - name: bar
                 value: bar
         itemProvider:
           $type: jcrChildNodeProvider
         forms:
           - name: foo
             properties:
               foo:
                 $type: textField
                 required: true
           - name: bar
             properties:
               bar:
                 $type: richTextField
   

1. Open the dialog and commit without selecting any radio button
2. The following error appears:

   ERROR nfo.magnolia.admincentral.AdmincentralErrorHandler: AdmincentralUI has encountered an unhandled exception.
   com.vaadin.server.ServerRpcManager$RpcInvocationException: Unable to invoke method click in com.vaadin.shared.ui.button.ButtonServerRpc
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:159) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:116) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:445) [vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:410) [vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:274) [vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:90) [vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) [vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1602) [vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:448) [vaadin-server-8.9.4.jar:8.9.4]
   	at info.magnolia.admincentral.AdmincentralServlet.service(AdmincentralServlet.java:119) [magnolia-admincentral-6.2.3.jar:?]
   	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) [servlet-api.jar:4.0.FR]
   	at info.magnolia.cms.filters.ServletDispatchingFilter.doFilter(ServletDispatchingFilter.java:148) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.CompositeFilter.doFilter(CompositeFilter.java:65) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.virtualuri.VirtualUriFilter.doFilter(VirtualUriFilter.java:98) [magnolia-virtual-uri-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.module.cache.executor.Bypass.processCacheRequest(Bypass.java:58) [magnolia-cache-core-5.9.1.jar:?]
   	at info.magnolia.module.cache.executor.CompositeExecutor.processCacheRequest(CompositeExecutor.java:66) [magnolia-cache-core-5.9.1.jar:?]
   	at info.magnolia.module.cache.filter.CacheFilter.doFilter(CacheFilter.java:164) [magnolia-cache-core-5.9.1.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.i18n.I18nContentSupportFilter.doFilter(I18nContentSupportFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.RangeSupportFilter.doFilter(RangeSupportFilter.java:78) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.security.BaseSecurityFilter.doFilter(BaseSecurityFilter.java:57) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.security.SecurityCallbackFilter.doFilter(SecurityCallbackFilter.java:84) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.OncePerRequestAbstractMgnlFilter.doFilter(OncePerRequestAbstractMgnlFilter.java:59) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.security.LogoutFilter.doFilter(LogoutFilter.java:94) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.OncePerRequestAbstractMgnlFilter.doFilter(OncePerRequestAbstractMgnlFilter.java:59) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.module.site.filters.SiteMergeFilter.doFilter(SiteMergeFilter.java:119) [magnolia-site-1.3.1.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.multisite.filters.MultiSiteFilter.doFilter(MultiSiteFilter.java:120) [magnolia-module-multisite-2.1.1.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MultiChannelFilter.doFilter(MultiChannelFilter.java:83) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.module.cache.filter.GZipFilter.doFilter(GZipFilter.java:74) [magnolia-cache-core-5.9.1.jar:?]
   	at info.magnolia.cms.filters.OncePerRequestAbstractMgnlFilter.doFilter(OncePerRequestAbstractMgnlFilter.java:59) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.security.auth.login.LoginFilter.doFilter(LoginFilter.java:127) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.enterprise.registration.RegistrationFilter.doFilter(RegistrationFilter.java:79) [magnolia-module-enterprise-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.personalization.preview.filter.PreviewFilter.doFilter(PreviewFilter.java:92) [magnolia-personalization-preview-app-2.0.3.jar:?]
   	at info.magnolia.cms.filters.OncePerRequestAbstractMgnlFilter.doFilter(OncePerRequestAbstractMgnlFilter.java:59) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:81) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.ContentTypeFilter.doFilter(ContentTypeFilter.java:155) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.ContextFilter.doFilter(ContextFilter.java:128) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterChain.doFilter(MgnlFilterChain.java:79) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.CompositeFilter.doFilter(CompositeFilter.java:65) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.AbstractMgnlFilter.doFilter(AbstractMgnlFilter.java:85) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.SafeDestroyMgnlFilterWrapper.doFilter(SafeDestroyMgnlFilterWrapper.java:107) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlFilterDispatcher.doDispatch(MgnlFilterDispatcher.java:67) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlMainFilter.doFilter(MgnlMainFilter.java:110) [magnolia-core-6.2.3.jar:?]
   	at info.magnolia.cms.filters.MgnlMainFilter.doFilter(MgnlMainFilter.java:96) [magnolia-core-6.2.3.jar:?]
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:9.0.37]
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:9.0.37]
   	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) [catalina.jar:9.0.37]
   	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [catalina.jar:9.0.37]
   	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [catalina.jar:9.0.37]
   	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [catalina.jar:9.0.37]
   	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [catalina.jar:9.0.37]
   	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690) [catalina.jar:9.0.37]
   	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [catalina.jar:9.0.37]
   	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [catalina.jar:9.0.37]
   	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) [tomcat-coyote.jar:9.0.37]
   	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-coyote.jar:9.0.37]
   	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-coyote.jar:9.0.37]
   	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589) [tomcat-coyote.jar:9.0.37]
   	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-coyote.jar:9.0.37]
   	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_121]
   	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_121]
   	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:9.0.37]
   	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121]
   Caused by: java.lang.reflect.InvocationTargetException
   	at sun.reflect.GeneratedMethodAccessor918.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.9.4.jar:8.9.4]
   	... 109 more
   Caused by: com.vaadin.event.ListenerMethod$MethodException: Invocation of method buttonClick in info.magnolia.ui.dialog.ActionButton$$Lambda$2228/555530089 failed.
   	at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:519) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at sun.reflect.GeneratedMethodAccessor918.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.9.4.jar:8.9.4]
   	... 109 more
   Caused by: java.lang.RuntimeException: info.magnolia.ui.api.action.ActionExecutionException: Action execution failed for action: commit
   	at info.magnolia.ui.dialog.ActionExecution.execute(ActionExecution.java:75) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionButton.lambda$new$d31ec881$1(ActionButton.java:65) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at sun.reflect.GeneratedMethodAccessor919.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:499) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at sun.reflect.GeneratedMethodAccessor918.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.9.4.jar:8.9.4]
   	... 109 more
   Caused by: info.magnolia.ui.api.action.ActionExecutionException: Action execution failed for action: commit
   	at info.magnolia.ui.api.action.AbstractActionExecutor.execute(AbstractActionExecutor.java:64) ~[magnolia-ui-api-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionExecution.execute(ActionExecution.java:73) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionButton.lambda$new$d31ec881$1(ActionButton.java:65) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at sun.reflect.GeneratedMethodAccessor919.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:499) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at sun.reflect.GeneratedMethodAccessor918.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.9.4.jar:8.9.4]
   	... 109 more
   Caused by: java.lang.IllegalStateException: Failed to write form state
   	at info.magnolia.ui.editor.FormPresenter.lambda$writeBindings$5(FormPresenter.java:130) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.HashMap.forEach(HashMap.java:1288) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormPresenter.writeBindings(FormPresenter.java:124) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.editor.FormView.write(FormView.java:148) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.editor.SwitchableFormView.lambda$write$2(SwitchableFormView.java:116) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.HashMap$Values.forEach(HashMap.java:980) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.SwitchableFormView.write(SwitchableFormView.java:116) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.Optional.ifPresent(Optional.java:159) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormView.lambda$null$5(FormView.java:151) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.HashMap.forEach(HashMap.java:1288) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormView.lambda$write$6(FormView.java:151) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.ArrayList.forEach(ArrayList.java:1249) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormView.write(FormView.java:149) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.contentapp.action.CommitAction.lambda$write$0(CommitAction.java:112) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.Optional.ifPresent(Optional.java:159) ~[?:1.8.0_121]
   	at info.magnolia.ui.contentapp.action.CommitAction.write(CommitAction.java:111) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.contentapp.action.CommitAction.execute(CommitAction.java:105) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.api.action.AbstractActionExecutor.execute(AbstractActionExecutor.java:62) ~[magnolia-ui-api-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionExecution.execute(ActionExecution.java:73) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionButton.lambda$new$d31ec881$1(ActionButton.java:65) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at sun.reflect.GeneratedMethodAccessor919.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:499) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at sun.reflect.GeneratedMethodAccessor918.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.9.4.jar:8.9.4]
   	... 109 more
   Caused by: com.vaadin.data.ValidationException: Validation has failed for some fields
   	at com.vaadin.data.Binder.writeBean(Binder.java:1744) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at info.magnolia.ui.editor.FormPresenter.lambda$writeBindings$5(FormPresenter.java:127) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.HashMap.forEach(HashMap.java:1288) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormPresenter.writeBindings(FormPresenter.java:124) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.editor.FormView.write(FormView.java:148) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.editor.SwitchableFormView.lambda$write$2(SwitchableFormView.java:116) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.HashMap$Values.forEach(HashMap.java:980) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.SwitchableFormView.write(SwitchableFormView.java:116) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.Optional.ifPresent(Optional.java:159) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormView.lambda$null$5(FormView.java:151) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.HashMap.forEach(HashMap.java:1288) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormView.lambda$write$6(FormView.java:151) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.ArrayList.forEach(ArrayList.java:1249) ~[?:1.8.0_121]
   	at info.magnolia.ui.editor.FormView.write(FormView.java:149) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.contentapp.action.CommitAction.lambda$write$0(CommitAction.java:112) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at java.util.Optional.ifPresent(Optional.java:159) ~[?:1.8.0_121]
   	at info.magnolia.ui.contentapp.action.CommitAction.write(CommitAction.java:111) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.contentapp.action.CommitAction.execute(CommitAction.java:105) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.api.action.AbstractActionExecutor.execute(AbstractActionExecutor.java:62) ~[magnolia-ui-api-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionExecution.execute(ActionExecution.java:73) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at info.magnolia.ui.dialog.ActionButton.lambda$new$d31ec881$1(ActionButton.java:65) ~[magnolia-ui-framework-6.2.3.jar:?]
   	at sun.reflect.GeneratedMethodAccessor919.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:499) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.9.4.jar:8.9.4]
   	at sun.reflect.GeneratedMethodAccessor918.invoke(Unknown Source) ~[?:?]
   	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_121]
   	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_121]
   	at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.9.4.jar:8.9.4]
   	... 109 more 
   

   It seems that validation is performed even though the field hasn't been shown.

Dev notes

In form's write method we call writeBindings which internally calls writeBean in Vaadin which internally triggers validation. Could we call other API from Vaadin that would skip the validation? writeBean and writeBeanIfValid both validate. writeBeanIfValid does not throw exceptions, but fail to write silently so even worse.

Vaadin shouldn't validate untouched fields, maybe we're touching those accidentally? Changes in defaulting behavior could touch those?

Consider not validating when no change.